I'm finding the German 6.0 BR tank lineup to be quite good fun at the moment, even though I've barely got parts for some of them!
2x Panthers and a Tiger - Panthers for all round speed, mobility, hitting power and a decent ability to bounce incoming shells, and a Tiger for if you need a bit more 'slugging' capability
Sadly I do seem to fight mostly 6.7's or higher with this lineup, but that seems to work out no matter what tanks I take, so these seem to be a pretty good combination.
I do love the massive smashing capability of the Russian big tanks, but that's also their biggest weakness. Go up against a pair of enemies, kill 1, then get killed. Get an injured loader, and wait half a match for a new shell to be in the barrel.
Just gets too annoying sometimes, because your team just sits in cover and waits for you to die, rather than helping out.