Ok, every unit needs a unique position to warrent its inclusion into the game and we would like to try and make it semi accurate.
Inf are the best defensive bang for your buck and all around cheapest unit.
Art are the best offensive bang for your buck, although I honestly think they need modified (maybe not with 6 IPC tanks though).
Arms have the 2 movement, that is there thing. Although I feel with mec inf as a 1-2-2-4, and arm as a 3-3-2-6, your going to see alot more mec inf than you will Arm. The new G1 buy (if art effect mec inf) will be all art, followed with waves of mec inf. For this reason I believe arm should be 3-2-2-5. Weak in the defense, but still offensive powerhouses.
Now for a heavy tank. Historically they were extremely expensive, extremely durable, a bit slow, and strong on the defense.
3-4-2 or 4-4-2 would be my pick, without the blitz ability (2 movement yes, but no blitz, not a big detail, but still) but can take 2 hits. Since this is modeled after a battleship so to speak, which is almost double the cost of a cruiser, they should be almost double the cost of a normal tank, 10ish IPCs. But with the 2 hit, would be really good in a strafe, or against multiple invaders. Would a ton of them be purchased? No, but some would be and they would have a nitch.