[name]Dexter[/name] - handsome and quirky! I like it a lot, although I slightly prefer [name]Declan[/name]. They don’t really feel similar to me, but I’ve heard [name]Dex[/name] used as a nn for both, and I personally prefer that. 
[name]Henry[/name] - love it! It’s so classic and handsome.
[name]Chester[/name] - a bit too old-fashioned for me still. Not really a fan, sorry.
[name]Milo[/name] - quirky and handsome! I like it a lot. I’m starting to think [name]Miles[/name] nn [name]Milo[/name] might be a more versatile option, though…
[name]Declan[/name] - ah, here he is! [name]LOVE[/name] this.
[name]Isaac[/name] - like a lot. If I had to pick a top four, this would probably be on it.
[name]Finlay[/name] - top three for sure! It’s such a handsome and cool Irish option, even if it is quite mainstream, and I’ve grown to love the -lay ending as opposed to [name]Finley[/name].
So handsome.
[name]Flynn[/name] - too close to [name]Finlay[/name], for me, but I do love it. This would probably be my fifth favorite.
[name]Theodore[/name] - I love [name]Theodore[/name] as a whole, but not really any of its nns. Maybe as a MN? I think [name]Finlay[/name] [name]Theodore[/name], [name]Flynn[/name] [name]Theodore[/name], or [name]Henry[/name] [name]Theodore[/name] would be lovely.
[name]Arthur[/name] - handsome, but I prefer this as a MN, too. It’s one of those names that is making a comeback and feels very in-style right now, but it still feels really old-fashioned to me (but somehow, I still sort of like it!). I’m not sure if that makes any sense, lol.
[name]Casper[/name] - cute, but I like [name]Caspian[/name] more.
[name]Finlay[/name], [name]Declan[/name], [name]Isaac[/name], and [name]Henry[/name] would be my top four–[name]Finlay[/name] and [name]Declan[/name] are my two favorites, and I can’t quite choose between the other two.
If you’re set on [name]Felix[/name], though, then [name]Felix[/name], [name]Declan[/name], [name]Isaac[/name], and [name]Henry[/name] might work better.