I *was* playing Allods Online (F2P microtransaction-based) regularly, until I sold my end-game character (four characters total in the account, just one being really end-game and well-geared for the time), made $300 out of it. Then a few days after that I started again, created another character on the opposite faction "for the heck of it", to play it casually, I still ended up spending/wasting $90 on it, then I stopped (recently), I haven't touched it since the past week (playing the original Witcher, DA Origins and War for Cybertron lately).
I never played WoW, ever (only saw a few very old game-play videos on YouTube years ago). I played RIFT this very week (thanks to the 7-day trial), made a character for both factions... I don't like it much, the quests are very generic "kill 'x' amount of 'y' foes", "gather 'x' amount of 'y' item", go back to the quest giver, accept quest. The story is uninteresting although the concept behind it is good enough (it's not a usual "good versus evil" plot, it's more about faith and belief, or lack thereof), it's interesting on paper but in the game itself it's not presented and narrated in any way that I'd find immersible, animations are stiff, some just look terribad, but I really like the performance even with maximized settings (except for the A-A, which I've set to the simple blur option, and the resolution being 1280x1024 which helps a lot with the frames rate).
Overall RIFT is "ok", I guess, I'm glad I'm trying it with the trial or else I'd have regretted buying it, I'm just waiting for Guild Wars 2. I don't think I'll play Old Republic, I've seen a recent video of it (around an hour or game-play) and it looked just as generic as RIFT with the difference being that the game has voice-over (and good voice acting I'd imagine) and set in the Star Wars universe which I don't really care about if it comes under the form of an MMORPG. I love Star Wars, but I'm extremely picky when it comes to the MMORPG genre itself.
The only subscription-based MMORPG I actually own is Star Wars Galaxies (vanilla, no expansions) which I bought when it was still relatively new (the first expansion was released I believe when I bought vanilla), I played that one for three months (two of which were paid from a game card that came with the game if I recall correctly), then I quit since I was just overwhelmed by the size of the whole game, the amount of things that could be done and the fact that I myself was completely new to the very concept of massively online multi-player stuff, I wasn't sure what to do or where to go, I followed some quest markers and so on, sure, that was the basics, but anyway I felt just irrelevant to the whole thing and I canceled my subscription before the fourth month kicked in (and I still have the game in my desk with the box).
Really the only MMORPG I'm going to play "seriously" will be Guild Wars 2 (never played the original, as a side note). In the meantime as far as MMORPG goes it's Allods Online, casually, and that's pretty much about it (and I'm getting really bored of it, although I've played it for a good seven or eight months now). I tried other F2P ones too, and really other than AO and WoT (World of Tanks) there's nothing worth it. I must say that for a time EVE interested me, but after reading some stories about how it goes in that game I just decided to ignore it completely (basically it's just a very harsh game, with hardcore players, not my kind of stuff).