Methinks people got distracted...to answer your question OP, here's the short and skinny:
Bard just got a major change to their playstyle dynamics. but since you haven't played one, it won't impact you as it was just a change to how they played in the past. Their DPS was low on HW release, but they recently got some nice buffs, and there's not enough real world (a.k.a not a target dummy) parses to know how they are doing overal. Bard's (and MCH) tend to do better in comparison with other DPS in real world situations then on test dummies, so don't trust the dummy parses at this point.
MNK has a very set and stable rotation, but relies allot on positioning and keeping their damage/speed buffs up. they are slow w/o the speed buff, but very fast with it. yoru going to be watching your position allot. NIN has less positionals (I think they got one in HW, thats about it), but timing is everything to their mudra's. outside of that, they are a very well balanced class right now...probably one of the better balanced ones in the game atm.
Both MNK and NIN are doing fine on test dummies and in real world parses. so your decision will rest more on which playstyle you like best. MNK - set rotation of 2.5 chains of skills, shuffling positions allot. NIN = timing mudras, more flexibility outside of that, less positionals (mudras can be a pain if you have bad latency, I will say that). BRD is more about adjusting to team demands, and paying attention to the team needs with your buffs.
