I played the beta, very enjoyable. There is a point where it can seem like grinding involved to get to each tier up however
I preferred the lower level tanks like the M3 Stewart as you get better match ups as a medium to highest level tank in the battles rather than the M5 Stewart where your the bottom of the barrel and cant even damage the 6 Tiger 2's you'll be matched up against for example.
My tanks were maxed out and I didn't bother buying new ones because a stock level 5 tank is so much worse than a pimped out Level 4 tank. I had a maxed PzIII, maxed M3 Stewart, and a maxed out Panzerjager 1 if I recall correctly (that thing was awesome though, able to rip Tigers and KV-1's new holes.)