My trip up teams is, and has been for 2 expansions, a trinity comp with hunters. I leveled it in both expansions thinking it would be fun because they generally do well. And indeed they do, but I just found it dull. Didn't help that I I chose a guardian druid tank, which I also found dull beyond belief.

Other than that I've not really had much issues... Some hit and miss class choises for mixed teams, but nothing that swapping 1-2 toons would not have solved.