Have got all three.
I find Stardrive disappointing - not so much in the lack of fulfilled promises (I bought later on, so I knew what I was getting), just that it seems a little...meh. Not shallow, per se, but just not as finely constructed as I would have liked.
SotS is brilliant fun, falls into the 'easy to learn but hard to master category', and has a good multiplayer community both here and elsewhere (so I've heard - I'm not a multiplayer man myself). Turn-based.
Distant Worlds is exorbitantly expensive, yes, but if you're looking for a deep single-player space 4X game then it's perfect. Detailed ship design, decent diplomacy, and solid enough that you can pretty much put the whole thing on automatic and just toy around with the bits that you like if you want (don't like designing ships? Let the AI do it, and focus on your colonisation strategy!) It's pausable real-time, not turn based.
Another one you might want to look at, though a bit different from the above, is AI War: Fleet Command. It's an entirely different style, though. Excellent game with lots of strategic depth to it, if you're a strategist. Pausable real-time.
Sins of a Solar Empire is an interesting RTS in space, if that appeals to you as well, but it's a different animal to all of the above.
As a long-time Space Empires player (oh III, I miss you) I find all of the above are fun at different times and for different reasons. Your mileage may vary.