I've been using the Spit MkXIVe to grind the vampire & venom over the past few days, the spit's great, it has a BR of 5.3 so although not a seal clubbed, is a match, if not slightly better than the majority of aircraft it comes up against regularly. Racks up the lions as well as its quite cheap to repair
For the Germans, I found the D13 premium was very good, but the Horton was excellent, especially in the ground attack role.
For the Americans, well I used the B29 to grind a lot of the jets, you usually get one aircraft kill & can wipe out a lot of ground targets with it, but before that, the p38 Lightning was excellent.
Anyone got any others?