In terms of stats, Roy, Eliwood, Hector, and Lyn always disappoint me to varying extents. The biggest problem with the FE7 lords is that no amount of training seems to adequately prepare them for the final chapter. (I think this relates to the argument that the legendary weapons are actually too statistically heavy for the characters to wield effectively.) Coincidentally, as characters, I really adore them. XD
Personality-wise, I really don't care for Marth. His old-school games are understandably light on story and characterization, but the new games have absolutely no excuse for being so poorly written. I know as much about Marth now as I did when SSBM came out. :/