It varies.
Admins work Day in and day out on a numerous number of things, and they keep shit together. (I can only imagine what Ryan does as Lead GM. It's probably tiring.)
Clan Mods have to manage every clan ever created as a whole. the job comes with great responsibility, knowledge, and work. It, in my opinion, is is probably the most intensive.
GameMasters have the most time consuming job probably. Monitoring In-game matters on the a frequent manner, hosting, banning, etc.
Devs create the game. there's that.
Market Squids do market things. Probably very time intensive.
Smods do SMod things.
The list goes on.
If you want specifics, any Admin.