Physical appearance, wise, my top 5 would probably be:
1. Chrom
2. Inigo
3. Gaius
4. Stahl
5. Frederick or Lon'qu (they're tied)
Frederick has a handsome face but I don't like how bulky his armor makes him look. It's not bad looking by any means but if the GK armor was slimmer it would look better to me. Lon'qu's handsome but his portrait looks weird to me with how you can only see him from the side. Makes him look too...two-dimensional.
But really, the only guys in this game I don't consider handsome are Walhart, Gregor, Gangrel and Ricken. And even then, Ricken's not even ugly to me, he's just not handsome - he's cute in a "aww look at that little boy" kind of way.
The cutest boys to me, though, are:
1. Donnel
2. Stahl
3. Male Morgan
4. Brady
5. Owain
These are based moreso on personality than looks, though I must admit I find Donnel, Stahl and Male Morgan pretty cute look wise too.