Mine happen to divide up quite nicely, as you'll see below!
Crows/Corvids:
These two are probably my favourite Flying types overall and mainly because I think crows are cool as hell. Corviknight just looks intimidating and sleek, with the metallic colour scheme and just by size alone really. Honchkrow has a funky looking hat and has a mob boss theme which is dope, plus the colour scheme just looks nice. I've used both before in playthroughs and both served me well so it all works out quite nicely.
Bats:
Bats are cool, and whilst I do like the OG Zubat line as well I just think these two just clinch it for me. Noivern has a draconic + sound theme which just works really well for me, and Gliscor just gives me the ol' childhood nostalgia from trying to draw it when I was younger. Plus Ash owned both of them are they were both loveable bat bois! What's not to like?
Big Ol' Legendary Flyers:
I'm playing through Johto (check out the Gen II recent happenings thread for that adventure) at the moment and dreading trying to capture Lugia and Ho-Oh, but they're probably some of my favourite legendaries from any Pokemon game. Ho-Oh just has an awesome colour palette and Lugia has the cooler looking design, I like them a lot. Rayquaza is my favourite Legendary of all time both as a Dragon and a Flying type because the movies made it seem super strong and I have fond memories of my friend giving me his from his Emerald playthrough (we transferred it to my Pearl version). Was awesome!
The Bestest Early Bird There Ever Was:
This thing was pretty good in my Sinnoh playthroughs (when I get to Platinum I'll probably use one) especially now I know that Return is actually a good move. Younger me was absolutely stunned that this bird could learn Close Combat and I really did like its plucky and combative attitude and design. It just looks cool, you know? So this is a solid birb choice.