I always have trouble replying in these threads since I can never define any single class as my favorite/least favorite as I find virtually every class to have a vital role in a team. However, I'm going to be stubborn and make a post anyway.
Favorites
1. Berserkers - love their extreamly frequent critical rate, insane strength, great speed and very high HP. Pure powerhoses
2. Valkyries - I thought I'd have a magic user (FE6-FE8 one I'm talking about obviously) as my #2 so I choose valkyries. I've recently come to love valkyries for some reason, and I like how they're mounted (sorry, couldn't give better reasons. ''I like how they're mounted'' is the worst thing I've ever said on this forum).
Least Favorites
1. Assasins - with this class I'm only talking about the FE6-FE8 incarnations since the FE9/10 assasin (Volke) is one of my favourite units over the 2 games. For a start I don't think they're a good promotion for theives since I don't understand how a 'promotion' for a FE unit involves a unit losing an ability, the rouge class is much better promotion for them. Also statwise they're nothing special, and the silencer skill doesn't really make up for it. Swordmasters are a much better sword unit.
2. Generals - I feel bad putting generals as a 'least favourite unit' since a lot of the time they are very useful (like I said . However they generally (pun?) don't fit into my style of play because of their low speed and movement.