But let me tell you why I play more as Germans:
First of all, I am German. (So I might be a bit biased.)
I like the smaller, but therefore better units more, same reason why I play Protoss opposed to the Swarm/Soviets.
I am all about efficiency. It is cooler to beat a bigger army with more advandced troops/tech.
The tanks: They have way better names^^ IS2=Joseph Stalin? Lame. Tiger? Marder? way "cooler"

And I love the German Tank design (not that big of a deal but for example the tanks in WoT. I just like the form and design more.) The Looks!
Also I am sure my Worldview (education, society, videos on the internet, cold war) gives me a negative Soviet image (no not because of the campaign, pls don't discuss about it here.) And with negative I mean not negative in general or about the people who live there!, but hmmm... . And here I am mostly talking about the modern world.
And because I have to deal with people who speak only Russian in DotA2, even if I am in the queque for ENGLISH language.