(I am noob but) It is very hard to say which faction is best because there are several situations you need to deal with: arty, heavy tanks, blobs. Defensive and Offensive stances.
Soviets have an answer to everything depending on how you tech. Maxims+Mines for blobs, Penal satchel + SU85s for tanks, Katy+ML20+IL2 for arty.
USF gets beat up early game but can make blobs, Jacksons, and Priests to do well late game.
BRITS get beat up mid game without snares and only one AEC. Late game they have Firefly+Churchill+Comet to deal with tanks. Bren blobs+Vetted vickers for blob control. They are weak in the arty.
But each faction excels in different scenarios. If you are in a defensive stance Bofors and Fireflys do very well. If you need to be aggressive USF blobs and Jacksons work well, especially after priest softening things up a bit. Soviets can go wither way maxim+Zis+SU85 for defensive or blobs+SU85+t34+Katy for offensive.
And in many cases pushing the right units out first makes all the difference. Like after a katy shot, send penals out for sight in front of SU85s. Panthers will not push for fear of satchel, etc. Or sending a cheap t34 in front so it gets targeted while your SU85s deal some damage.
My point is no matter what, once you are in game you will wish you had picked a different faction
