- Airborne - the P47 loiter is quite potent lategame, and the elite infantry is strong too. Also paradropping MGs/AT guns is nice.
- Pershing doc - I've seen this but it might not be the best on all maps, due to the abundance of german tank destroyers. But the pershing is very strong.
- Infantry doc (with priest) - this is a staple in 2v2 - Scotch uses it in 100% of his games. the M1919LMG is very strong on rifles, and the priest is an excellent howitzer piece. Mortar halftrack used to be amazing but now it's mediocre I'd say.
- Rifleman (with the easy 8) - I've seen this a little little little bit. Easy 8s are a nice generalist tank if your mate is making specialists (firefly/su85/jackson)
Right now no one picks armour, and recon doctrine seems super rare too. I am reluctant to even mention Rifleman doctrine on the list above since I think it's really the first three that you see. Ever since the Calliope was nerfed a few patches ago, that commander is also pretty useless. Calliope is just an expensive and shittier version of the Katyusha.