My favoured concept for an ideal reuseable satellite launcher would be to use fly-back boosters for both the central core and the straps-ons, using methane/LOX propellents, preferably with detonation engines to maximise energy efficiency. The strap-ons would peel off at a relatively low altitude once the stack is clear of the bulk of the atmosphere, and proceed to fly back to an airstrip next to the launch facility. The core would continue to burn until stage seperation, and may need to use a set of air-breathing (ramjet) engines to burn residual fuel and provide sufficient cross-range capability to reach an airstrip, depending on the launch location and the flight trajectory.
The 2nd stage would be augmented with a winged or lifting-body structure, equipped with thermal re-entry protection, and designed to enter a fractional orbit before the 3rd stage is ignited (comprising a small expendable stage and the payload or manned vehicle). The 2nd stage would de-orbit after < 1 rotation and proceed to re-enter and land at an airfield as per Buran (or its inferior Murkan copy
). Not a heavy flyback booster like Spiral, but a half-way house design.
It wouldn't fit every mission profile of course, but for routine delivery of piloted vehicles and medium satellites to LEO it would be ideal.