im going to say the straight flushes are more likely. for quads vs quads you need the community to either be 2 pairs or a pair and a set. im thinking that the fact that the community cards, and the two players cards would all have to be the same suit would make this more difficult. you could calculate it by first calculating the possible communities. for example, the flop for the quads one would have to flop a pair no matter what, so the probability of this would be 1-((48/50)(48/50)) i think