I don't really care which world is bigger than the other, what I do care about though is how the worlds feel.
I'm level 46 and so far, SWTOR has felt like a big loading screen fest. Of course, I didn't expect to be able to traverse an entire galaxy without any loading screens, and I didn't expect to be able to explore entire planets, but I still feel like BW could've crammed in less loading screens at some places than they did.
It also feels like all worlds are railroad. You have no reason at all to stray off the beaten path. If you feel like exploring, you're wasting your time doing so, because the entire planets look pretty much the same everywhere you go. The differences are pretty vague at best. You reach Dune Sea and suddenly there's elevation in the terrain. You reach northern Belsavis and you see snow instead of jungle (we already had that in WoW). You go from one place on Coruscant to another, the only difference is that at one place the sun is shining and at the other it doesn't.
WoW to me felt like a full, entire world, free for me to explore. No restraints (though of course they were there, but they were cleverly masked, more than can be said for the worlds in SWTOR) to where I could go, something was waiting beyond the horizon. SWTOR feels like they did Cataclysm formula with zones scattered all over the place, and could be traveled to through loading screens. Only difference is that the Cataclysm zones are still connected to the rest of the world.