Basically if I want to raid or play with other people or even play a good PVP MMORPG I would play WoW without doubt
But, I got bored of all that and i'm a big star wars fan and i love the lore and story of the saga so SWTOR it's a perfect game for those like me who have been waiting for KOTOR 3 or want to develop SW classes with their own rich history in a massive universe.
However I do miss from WoW that feeling of open world you get by being able to freely travel by foot, or flying or sailing through the maps. I hope they bring that to SWTOR in some patch in the future.