well, to be honest it's always been pretty much situational up until the 3rd~4th week, when everyone has gathered enough points and the overall rankings start to settle down little by little.
but even then, it all depends on luck with match making in the end.
you either get lucky and find an "easy" target, or you end up with a counter-class that can potentially screw your points up.
anyway, my current bets are on these:
dark avenger - erky
TH - anytime/poseidon
Necro - ripwalker
Warlock -fusso
sws -bizzqquit
spellsinger - sjeks
silver ranger - modoy
shilien knight - sayomi
phantom sumoner -trashlord
not going to mention the other classes, as there's no point in my opinion.