The ones I’ve been playing on and off over the past few years are Guild Wars 2 and Lord of the Rings Online.
GW2 is a really nice game to just pick up and play without needing huge time investments. It has a fun gameplay loop and well designed zones to explore. Haven’t gotten around to playing the new expansion yet, but I hear it’s pretty good.
LOTRO is great for that traditional MMO experience. The community is very friendly and surprisingly active. It has a nice atmosphere. They are also frequently giving away the expansion packs, so you get a lot of content for free.