In the terms of Frontal Aspect protection against Armour/Infantry/Airborn targets, I'd say the T-90 has it better off against the M1A2 Abrams.
Comparing the 2 in Protection:
Kontakt-5 or Relikt Heavy ERA
Shtora Electro/Optical jammer
Nakidka signature reduction suite
ARENA Active Protection System possible
Depleted Uranium Mesh
Electro/Optical jammer possible
In perspective, Chobham v.s. modernized Combination-K, the M1A2 Abrams has the best baseline armor. However, because the T-90 is supplemented by advanced ERA and the Abrams is supplemented by a DU mesh, they are both comparable on the hard armor aspect of it. But, because Shtora comes standard on Russian T-90 tanks and the Missile Countermeasure Device isn't standard on the Abrams, against SACLOS guided ATGMs, the T-90 has it best.
But, the U.S. doesn't use SACLOS guided Hellfires as much nowadays and have been making the move towards the Longbow Hellfires, that puts the challenge on the T-90. However, the T-90 has 2 things that can stop the Longbow Hellfires. The first of course, could be ARENA. Although ARENA isn't standard, it would knock out the Hellfire before impact. The second, is Nakidka. Nakidka would basically reduce the RCS of the T-90 by about 6 times according to their designer.
A Longbow Hellfire v.s. an M1A2 Abrams is a different story. The Abrams does not have a signature reduction suite like the T-90 has. It also does not have an APS system ready. If a Longbow hellfire was used against the Abrams, there would be a high probability of impact, medium-high probability of penetration, and fair probability of lethal impact. Really, until Quickill is introduced in a few years, air attacks will remain the highest lethality threat to an Abrams.
That was the airborn threat assessment, against Armored and Infantry, we should put something into perspective. The M1A2 Abrams can fire the M829A3 for Tank on Tank engagement schemes. The newest APFSDS round used by Russian tanks is the 3BM46, however, information on ti is limited. So for this comparison, I'll be comparing the 3BM42M against the M829A3.
The 3BM42M is a long rod penetrator composed of WHA(Tungsten Carbide). It's Length to diameter ratio is 22 and thanks to the longer gun of the T-90, has a high muzzle velocity of about 1750 meters per second, with a muzzle drop of about 50-100 meters per kilometer. The projectile after the sabot is released weighs about 4.8 kilograms. Penetration estimates using the Odermatt formula comes out to about 600 meters RHA equivalent penetration at 2,000 meters with target slope of 0 degrees.
Against the Frontal Armor of the M1A2 Abrams, I am not confident of a lethal penetration at 2,000 meters or more. However, WHA projectiles will almost always be more lethal than a DU projectile at ranges over 2 km. But, the heavy protection provided by the Abram's mix of Chobham and DU might eliminate that advantage. However, Chobham is notorious for having a bad multi-shot capability, so my guess would be that several 3BM42Ms fired accurately at an Abrams might produce a lethal penetration.
The M829A3 is also a long rod penetrator. It is composed of a "super DU" alloy that is less prone to shattering. The L/d ratio of the A3 is estimated to be about 27, which means that it is longer, skinnier, and thus, more potent for penetration than the 3BM42M. Muzzle velocity is about 1555 meters per second and probably has a similar muzzle loss compared to the 3BM42M at 50-100 meters per kilometer. The projectile most likely has a similar mass compared to the 3BM42M, and tank nerds have estimated it to about the higher ends of 4 kilogram. Penetration estimates come out to about 790 mm of RHA, and I'm going to take a guess that the range was 2 km and the target slope was 0 degrees.
The M829A3 is a good weapon, but I would have to say that if fired at the Glacis of a T-90 at 2 km out, there would be a small-medium probability of penetration and a small probability of lethal penetration. This is due mostly to the effects of Heavy ERA, which is only enhanced by even heavier ERA like Relikt. Robb McLeod(sp) estimates that Kontakt-5 would reduce the penetrative capabilities of APFSDS rounds by around 30%. However, that is not taking into question the super DU alloy used by the A3. But like the 3BM42M, if the Abrams crew does manage to land a few hits on almost the same places, that there would result in a penetration and possibly a lethal one.
Against Infantry, assuming the Infantry are firing RPG-7s - RPG-29s - Kornet ATGM - Javelin ATGMs, I'd also have to say that the T-90 has a better chance of preventing a penetration compared to the Abrams. For this comparison, I will not take into account ARENA APS. The RPG-7 is a proven weapon that has been used in many places so this is the most common scenario. When fired on the Frontal aspect of either Tanks, expect no penetration. When fired at the Top/Side/Rear of either tanks, expect penetration. Although, the Abrams has been proven to withstand a hit or so on those aspects, it in general is not guaranteed protection against it.
RPG-29 wise, expect penetrations on both tanks, all aspect, save Frontal aspect of T-90. The RPG-29 has penetrated the Glacis of 3 of the most advanced MBTs in the world, so it's quite battle proven. The T-90 would be saved by it's ERA, which(as stated by Nii Stali) provides 600 mm of RHA equivalence protection against HEATs and Relikt would provide double that or 1.2 meters of RHA equivalence of protection against HEATs. In case you're wondering why the Tandem warhead might not penetrate Kontakt-5, it's because Kontakt-5 has a thicker front metal plate, which means you'd need a bigger precursor charge.
ATGM wise, the Kornet has penetrated(but not lethaly) the Armor of the Abrams during the Iraq war. It has also been used against the Merkava IV tanks but I cannot remember how successful it was. Now assuming that the Abrams does have the Missile Counter Measure device, I highly doubt that it would be able to jam the Kornet's guidance system as it is a beam rider. However, if the Abram knew it was being fired upon, it could simply shoot a smoke grenade which would most likely throw off the Kornet Gunner's Thermal sights leaving the Kornet to flabber around aimlessly.
Against the T-90, Shtora also wouldn't be able to jam the Kornet, and a hit to anywhere other than the Frontal aspect might lead to a lethal penetration. However, Shtora would be able to realize it has been painted by the Kornet's gunner and would therefore automatically fire it's smoke grenades which has the same properties as the Abram's smoke grenades. One more thing to note is that Nakidka also reduces the thermal signature of the T-90 so there would be a smaller probability of engagement between the Kornet v.s. T-90 compared to Kornet v.s. Abrams.
The Javelin would be a different story as it is a heat-seeking, top attack ATGM. In performance wise, it is similar to the Kornet in penetration but has a bit shorter range. However, it is considered more lethal due to the weakness of the roofs of tanks. This is where the advantages of the T-90's multi-layer protection system comes to play. Both Shtora and MCD would be inactive as both would not be able to sense that they have been targeted. The best defense would be to launch a smoke screen, as that would throw off the seeker warhead of the Javelin. But due to the tank's inability to sense that it has been targeted, that would be very difficult.
When fired in it's Top Attack mode against the Abrams, I would have to say that it would result in a penetration, and most likely a lethal one. Against the T-90, it's very, very different story. The first thing would be that T-90's can be fitted with Nakidka, which does reduce the Thermal signature of the T-90, making it harder for the Javelin to effectively seek out and destroy it. The next thing is that the Russians also put Kontakt-5/Relikt ERA on the roof of the tank, which would severely dampen the penetrative attributes of the Javelin. Finally, if ARENA is installed, there's a high probability of intercept of the Javelin before contact with the T-90.
So, here's the score card(in my opinion) of protection compared to both tanks.
M1A2 Abrams v.s. Longbow Hellfire(fired at 8 km, open field, high visibility environment) - Fair-High probability of penetration/lethal penetration.
T-90 Vladimir v.s. Longbow Hellfire(fired at 8 km, open field, high visibility environment) - Fair probability of penetration/lethal penetration.
RESULT - T-90 has a better chance of escaping from an engagement with the Longbow Hellfire. T-90
ARMOR v.s. ARMOR
M1A2 Abrams v.s. T-90 Vladimir(2 km open field, frontal aspect engagement, high visibility weather, APFSDS rounds) - Fair probability of surviving 1st hits to Glacis armor for both Tanks - [bTIE[/b]
ARMOR v.s. INFANTRY
M1A2 Abrams v.s. RPG-7/RPG-29/Kornet/Javelin(Urban environment, AT weapons fired at maximum range, single shots, variable aspects) - Low probability of all aspect penetration/lethal penetration by RPG-7. Fair probability of Frontal aspect penetration/lethal penetration by RPG-29, High probability of Side, Top, Rear aspects penetration/lethal penetration by RPG-29. Similar probabilities of Kornet v.s. Abrams. High probability of penetration by Javelin, all aspect.
T-90 Vladimir v.s. RPG-7/RPG-29/Kornet/Javelin(Urban environment, AT weapons fired at maximum range, single shots, variable aspects) - Low probability of all aspect penetration/lethal penetration by RPG-7. Low probability of Frontal aspect penetration by RPG-29, High probability of Side, Top, Rear aspect penetrations by RPG-29. Low-Fair probability of penetration, all aspect for Kornet(low probability on at Frontal aspect). Fair-High probability of penetration of Javelin, all aspect(High probability penetration, rear aspect).
RESULT - T-90 has a better chance of surviving from an engagement with the Infantry AT weapons. T-90
Of course, that wasn't a professional analysis and I'm probably missing somethings or wrong on others. Remember, this was analyzing each Tank's levels of protection. That is not to say that if a round does penetrate, both will survive. The T-90 has some risk of a catastrophic explosion if the round penetrates(although this is disputed). So, remember, that was only about protection, not survivability.