A railgun LITERALLY cannot put something into orbit. It can do suborbital trajectories, and it can theoretically do escape trajectories, but orbits are impossible. You end up with an apogee of however high, and a perigee of SEA LEVEL. Bare minimum, you need a rocket to raise your perigee above the atmosphere. And since the ram pressure during launch would be so tremendous, in practice I doubt a railgun can be built that breaches the Karman line with a worthwhile load.
Skylon is a very, very high-risk proposal. An air-breathing rocket needs to maximize the amount of time it spends in the atmosphere, thus it follows a much more depressed trajectory, thus reaching far, far higher speeds while still in the atmosphere, and the end result is that the thermal load placed on the craft is tremendous. And because Skylon burns LH2, it's an extremely bulky vessel as well, which exacerbates the problem.
SpaceX is following a calculated path. The first-gen rocket was tiny, and completely conventional. The second-gen rocket used a conventional layout, conventional fuel, conventional combustion cycle, but it did everything extremely well. It has the highest thrust-to-weight ratio of any rocket, and the highest specific impulse of any gas-generator LOX+RP1 rocket. They've been slowly pushing towards first-stage reusability, which gets you 90% of the benefits of SSTO, with none of the drawbacks. Their planned third-gen rocket is absolutely massive, uses a cutting-edge combustion cycle, and burns an innovative fuel. They aren't instantly revolutionizing the field, but they're on track to do it.