FE6: Lot was decent at best and Wade was pretty bad. Really inaccurate though.
FE7: Dorcas and Bartre were pretty bad. They had awful speed and have a hard time hitting. Never used Geitz so I can't say anything for him.
FE8: Garcia is a pretty good unit. I usually go Hero for the speed and swords, because Hand Axes > Bows. I always make Ross a Pirate over a Fighter, so I don't know if he makes a good one, but he sure does make a great Berserker.
FE10: I haven't played much of this, but Nolan is pretty good. One of the few fighters I like using.
FE13: I've used Vaike a few times, and he makes a much better Hero than Warrior. As a Warrior, I felt he had a hard time taking hits and bows aren't very helpful when Hand Axes exist. Postgame-wise I go Berserker for him.
I'm hoping Arthur is a good unit because I want to use him for Nohr.