I'd suggest having a look at UDK (Unreal Engine), simply because you'll be able to release the game as a standalone install rather than a mod, which will always limit your playerbase to some extent, otherwise. I don't think, Source is a good choice, as the engine is pretty old now and after two years of mod development it certainly won't look much better than it does now. At least it has a far bigger community than Crysis simply because there are so many Source games out there all giving you access to Source-based mods. I'm not a big fan of Crysis, both gameplaywise and regarding its bad performance and I believe it's also much better suited for outdoor shooters.
Anyway, don't base your decision on a user vote... have a look at the available engines, maybe do some prototyping and evaluate for yourself, what is easier to work with and what gives you the best results for whatever you're going for.