The only mmo's I ever really spent any significant time with were FFXI (on dial up for most of the time I spent with it so my experience wasn't great) and GW2. not mentioning eve... we dont talk about that..
There was a free MMORPG called Planeshift (I played quite a lot in 2005 or so, it's still around and being actively worked on) that was very elder scrolls inspired, I put a lot of time into in the past too but being a small free amateur project it didn't have a lot of players.
I just don't have the time or motivation to give modern MMOs the attention they really need to make progress, and I was very much a solo player at the time so progress was slow and hard.
I think if I was to pick up a new one it would be FF14, it has a balance of open gameplay and story which a lot of mmos ignore, it seems like a good community but as with all mmos they really dont want you to just drop in a play a couple of hours every second weekend, they want you to get in daily and stick to a routine, which I just cant commit to these days.