Germans are by far the best. Everyone should switch to them. Please. I need more German bases out there so I can get some salt.
Seriously, check your national goods in the storehouse. What you see the most of is probably a good reflection of each nation's popularity. I always have max marble, so I guess a lot of players are Roman for the 10% extra troops. I also usually have max porcelain, so Korean is a popular nation. It is strong with the boosted shooters and extra tactic, but I think it is more because the game is very popular in Korea and players are drawn to their own real-life nationality. I am always short of salt, and timber (British) is in the middle. Cheese (French) is weird; sometimes I am full and sometimes run low.
I started the game as British, and have not switched. I have a second base that is French, and I think it will be stronger once I get it to Global, because those French tanks are almost as strong as a factory heavy tank, for less than half the troop space. If my second base works out, I might switch my first base to French, but I do like those British shooters, and the extra loot is really useful. On my British IA base I use 3 tanks, 5 artillery, 1 supply cart, 50 shooters, 12 infantry. I use the infantry to clean up outlying buildings, or literally as cannon fodder to distract cannons. I ask for tank donations.