My first choice:

[BGs_Ricky]

Voted RAF, as I first started flying Hurries and Spits in COD.

Otherwise I don't have much preference, I'll fly both sides equally, Im starting now to fly the 109 a lot (being Swiss I like the E-3 a lot).
Next will be the 110, then Stuka and bombers.

What I like in COD is that I'm really enjoying learning each plane and taking some time to master it a bit before jumping to the next one. I still haven't dropped a single bomb in the game, so there's a lot I still have to do.

Back in the days of Their Finest Hour on the Amiga I loved to bomb ships in a Bf-110 as part of ErpGr 210, looking forward to do it in COD too