Best troops are Commandos, Mech Inf (sort of), Tank Destroyers, Tac Bombers, Strat Bombers, Destroyers, SP Artillery, Paratroopers (technically +10% Hp but no-one really uses them), and any nuclear stuff.

Mix in some ACs for scouts and you are good to go.

Med tanks are hella slow, that's why. And anyways the SP arty should deal with any other enemy tanks. Keep the tank destroyers in front of the arty, and suddenly their only choice is to either walk into your TDs or run for their life.

I would personally say tank destroyers mech Sp anti air Sp artillery and Sp rocket plus bomber support

The "BEST" units regardless of doctrine are those that effectively counter your enemies units. There are no "BEST" units for every situation. (except for maybe aircraft) If your enemy is using TD (as have been suggested they are "BEST") I would counter with Infantry/Commando and supported by Arty. Also it really depends are you attacking or defending. Armored Cars are the best defensive unit in the game but used effectively it can also be the best offensive unit as well even tho it its stats on offense are marginal at best. Thinking outside the box will let you use units in ways your enemy isnt expecting and therefore has no counter for.

Agreed

sp artillery

tanks aren't that useful as the other doctrines have more powerful tanks

get nukes the day you are able to get them, with the allied doctrine you get the nuclear bomber 2 days earlier