There are different kinds of guilds. Some are geared for PvP, some for PvE, some are for leveling and some are just casual guilds. You probably want a casual one, if one at all (as Sunni says, you don't even need one- the dungeon finder helps with that). We could all start a Cantr one on some server and just sit around chatting all day.
There are raiding guilds that take it seriously and have schedules for when they run their raids. Some PvP guilds have schedules for when they go and do the PvP stuff (I'm not much of a PvP person, so I don't know much about PvP outside of battlegrounds and trying to hide while questing). If you want into the top guilds of those kinds, then they usually require logging in at those times and somewhat regularly.
The one I'm in is a raiding guild, but it's a casual raiding guild (I definitely don't get into much raiding- no time). It mostly just depends on how you want to play and what the people in that guild have accepted as their requirements.
The pandas are cute. You should see them, BC.

I do understand getting burnt out, though.