Take my opinion with a grain of salt, but this is what I tell all my friends.
America: I don’t care for the props, I hate boom and zoom, and it is very monotonous. Early jets are good, unfortunately the uptiers are dreadful. Then Rank 6 and Rank 7 are back to relying on boom and zoom and missile spam. Rank 8 and 9 have amazing aircraft, unfortunately American mains are just dreadful so yeah. Beyond the BVRing F-15s (which can still fight if you have two braincells), the F-16s are amazing (especially since Gaini3ng nerfs the Grippens, Euros, and Rafale), and the F-18s are more renowned for 1v1 dogfights than actual Pub 16v16.
Russia is one of those nations that has one or two great planes while the rest of the Rank is trash, but still get called OP. Honestly, just grind out the MiG line, and use the leftover RP to grind the Sukhoi line until you get the Su-27. The rest of the tree is trash besides WWII Yak props.
Germany: has great props, but then becomes America and Russia copy paste, plus they have the weakest Eurofighter, which is hilarious since their tanks are OP for no reason.
Britain: Britain is amazing until Rank 6, then you’re depressed until you get the Grippen and Eurofighter.
Japan: amazing props, sucks from Rank 5-7, only gets good again at Rank 8.
China: copy paste Russia and America until Rank 7, where they become weaker Russian vehicles. But, you get a saving grace in the Mirage and J-10.
Italy: weaker Germany. Just Germany but worse variants of each vehicle. Even the Hungarian Grippen sucks because they get 120As.
France: basically just a weaker Britain, which is basically how their tanks are too. Rafale was great until the forums whined about it instead of realising how easy it is to beat them.
Sweden: pretty good props, decent early jets, sucks from 8.0-13.0 where your only good jet is the MiG 21bis. Basically only grind to the MiG 21 and only use that until you either get the F-18 or Grippen. Gaijin needs to buff the Grippen.
Israel: France and Britain copy paste until Rank 8, where you get the American copy-paste. Weirdly enough, the A-4 for Israel is probably the most fun you will have in the early Cold War era jets.