I would suggest for the best HT/gaming experience you go with one that has at least a 12" driver as anyting smaller lacks the volume to move enough air for great effects.
I agree with what Jakewash said. I tried the EP175 with 10 inch and it didn't do it for me, but the EP350 works just fine, if you decide to go with an Axiom sub.
Thanks for the advise, I'll try to stay away from 10 inch subs. For a sub it makes sense, since the bigger it is, the lower it can go.
What is your budget and how big is your room is a good start? Most likely ID would give you the best bang for your buck or looking into the used market, another option if your so inclined are DIY kits.
Room is approx 11x18. I haven't fixed a budget now. I don't see myself paying going over 1k$ however. Now, I don't want to spend 1k$ if I can't justify it. I'd rather pay something like 500$ esp. since I don't feel I'll really be able to crank it as much as I'd like in an apartment. So I'd be looking for some "best bang for the buck" subwoofer, I guess. However, I don't want to buy something that I will later regret buying, so if it's really worth paying more, I'd rather pay more.
As for kits, I don't know. If the build time is not too long, I guess I wouldn't mind... it could even be fun.