Tark Pros: HOF coaches in the D2 and D1ranks. Populated world. If you like D2 and D1 with good competition, this is the place to be.
Tark Cons: Less chance at Big6 jobs due to the competition. D3 isn't that competitive.
Knight Pros: D2 is pretty competitive. D1 looks to be pretty empty, so if you want a Big6 job, I'd think it would be easier to get here.
Knight Cons: D3 is not competitive, its fairly empty, and D1 is fairly open as well, so if you don't like playing against the SIM a lot, this isn't for you.
Phelan Pros: D1 is pretty competitive, so is D2, can't say about D3.
Phelan Cons: None really, except I don't see why one would pick this world over Tark really.