I play both WoW and SWTOR. I have an active account on both.

WoW have a good base content with a good base amount of players. But let's face it, the current deathwing content is pretty much killing the franchise. They maintained a good number of their 'active subscriber' base on sheer influence of D3 promotion they gave out a while back. I myself would've unsubscribed and see how MoP fixes up the problem later on.

SWTOR have a slightly better storyline base for PVE (I would say great, but I wouldnt' wanna be accused to be a fanboi). PvP aspect's still being fixed (OP classes being OP in 50, melee classes being kited to death etc), PvE glitches being actively fixed. (I count 2 server patches last week alone).

SWTOR have a clean slate. It's being cleaned up, and to be honest, I think it'll turn out great.
WoW is nice, but slowly turning into a big mess that blizz's trying frantically to fix up since ICC. If MoP's not gonna be a major reset (which judging by their talent system, is pretty major), I would pretty much give it up to be honest.

As for TS's question on good free online game, no, there is none other than a huge time grind that you'll eventually discover you'll have to put in money one way or another just to keep up. There is no 'free' good game out there. Just when you'll pay for it and how.