I'll just tell you what I did. I went up the same TD line you are. Get the T30. It is amazing fun. The T110E4 is good too, but I still find myself going back to the T30 for a good time. I then went up the T69/T54E1/T57 Heavy line. This is a strange line because it changes categories so much (light, to med to heavy) but I've had fun along the way. Each tank requires a new play style. The T71 is entirely different from the T69 style of tank. The autoloaders can be frustrating with their seemingly low pen (without gold) and long reloads, but once you figure them out, it is fun to deal that much damage that quickly. I'm about 500,000 credits away from the T57 Heavy. Be aware, that they are nerfing the T57 at some point, so if you don't want to do all that work for something that might not be as good when you get there...it is something to think about. I am just now going up the T29 line. I haven't enjoyed it much up to this point (I have the M6). If I were you I would just skip right over the to T29 from the M4E2 I will likely stop at the T29 because it seems to be a god-tank at it's tier, and none of the higher tier heavies interest me.