Ooh that's hard.
In No particular order (should they be in order? choosing 10 was hard enough) and again with no comment.. yet:

1. M4 Sherman
2. Matilda 2
3. Churchill
4. Panzer IV
5. Panzer V
6. Pz.38t
7. T34
8. Comet
9. M5 Stuart
10. Somua S35

And I'm still not happy with 2 or 3 of those.
Cheers,
Adam.