Wow those are all really good guys. I personally think though that maybe a logo with a P-51D in US Markings, a Spitfire in RAF markings, Bf-109 in Luftwaffe markings, and a Il-2 in Russian Markings and a Zero in Japanese markings would be awsesome on the logo. That sort of represents the 5 major powers.
If only 2 aircraft can go on it I would put a RAF Spitfire and Luftwaffe Bf-109 or a USAAF B-17 and a Luftwaffe Fw-190 or Me-262.