This is my basic analysis of the 3 countries, (France doesn't count as a country)
These are based on Tiers 1-4
US tanks- Have very good armor, decent speed but most have a rather small gun compared to Russian and German counter parts
German tanks- Have decent armor, horrible speed, and sport very impressive main guns.
Russian tanks- Have decent armor, above average gun, and are fast as hell.
French tanks- They are worthless unless you buy gold.