Depends how you define dominant. If you're looking at the length of time they've ruled the wilderness consecutively you'll have to say MM / FOE and perhaps EOP in 2011 for a few months if we're talking about F2P.
If you're looking at pure strength over a short period of time, you'd have to say FOE in P2P, MM in F2P and perhaps Epidemic for the 8 or so weeks they were #1 in F2P.
I haven't really been around OSRS too much, but IIRC there was a time where FI were just beasting it all, but I think the max pull was like 50 cuz the community was in a slump.