I can't tell anything about SWG since I never played it.
I enjoyed playing AO for quite a long time, but eventually got bored with it, mainly because reaching 220 implies a lot of farming, and because good stuff only drops rarely (IMHO). To be honest, I played AO a bit longer than I expected, because playing it with Legion was awesome.
As for WoW, I only played it on a smaller scale than what Legion does on the US servers (played it on EU servers with local friends, in a guild of around 40 people), but the same issue that got me bored of AO made me quit it aswell : % based droprates, that have to be shared among several people, making equipment farming a bit too tedious for my taste. The WoW PvP gameplay seems way too objective-less to be attractive, not to mention the fact that once more, fights are %chances to hit driven.
I recently reopenned my EVE Online account, and I think this game deserves some attention. If the first few hours/days playing it might seem 'slow paced', I do like the fact that fights are less luck-driven than other MMOs (well, luck does count, but chances to hit are not depending on a 'flat' curve, but rather a 'bell shaped' one that is more predictable). I do like also the fact that most equipment is available in the ingame market, thus removing the intensive farming mandatory in other MMOs. The skill system adds another good point to that game : Since you do train skills even when you are offline, mixing HCG with casual people seems easier than in other games. Last but not least, EVE PvP looks very promising, territories can be claimed, and huge alliances are warring each other out on a daily basis (check this
Map to get an idea of involved parties).
Hope this helped,
Regards.