Depends on what you need, but I agree with Spin that Quad tends to be better against OKW (at least an OKW player who is going heavy on infantry and/or being blobby). Especially if they already have a few shreks out since its a bit easier to kite and do damage with the Quad.
T-70 is much better if it's a larger map that has flanks - T 70 really shines as a flank patroler that can chase down lone squads and wipe them on retreat. T-70 is also a much better choice as a shock unit to push an early advantage. It's also more nimble (I had a game yesterday where I managed to circle strafe 2 Paks to death with a T-70 lol)
