Depends.
If you have mad skills (and I do mean mad as in you managing to go toe to toe with the best arena players and whooping em any day) you could go for the elite teams... problems are with them is they rarely accept new people, tend the be the biggest assholes is the game (exceptions ive seens are ns,=V=, and =[A]=)... and with that many idiots on one team they have stablity issues... as well as massive egoes.
the other choice is the middle teams who can excel and who have been around longer than all but a few of the elite teams and stock a few more down to earth people... Geez,BEE,AC,DoM,UNS,4M,Kin,DxM,oV,OX,Soup,UF,sCs,MA and many others that are either still in T2 comp or going on to tribes V... these are the teams that imho really make a ladder...some times they can go toe to toe with an elite team and win.
If you havnt been in the game very long ( 1-2 years ) or are just not that good yet you should try joing the upstart teams who at least have some idea of what they are doing and dont suck... because even the middle teams have a very skilled base.