You can fly every faction - each faction have cool planes on specific tiers.
For example:
-Germans: Great Bf 109, with the next patch allowing adding 2 20mm cannons they will become more epic! Me410 with its 4 cannons is also really nice, but rather use it to chase bombers than dogfighting, however ifare lucky you can also get many kills when theres chaos, because it simply smash everything with single burst! Currently on lvl 11 and heading to lvl 13!
-British: OP Beaufighter, cool Spitfires, I've bought also Typhoon which has nice reward and Wellington which has really high reward as a bomber; already flying at lvl 7 and I'm aiming to 8, in order to get 2nd Spit and thats all!
-Americans: Spam of Aircobra with its 37mm on early tiers really gives you advantage, however I'm currently on lvl 4, so don't have much experience with this faction
-Japans: In my opinion the most difficult faction at early tiers, however when you get this Heavy fighter Toryu, the life will become much easier! I'm currently at 5 lvl!