in terms of the termi's, i dont mind the old smaller ones, aslong as they are based on 40mm bases, as this does make a difference in combat (with me playing orks)
with 40mm bases i can get at least 2 orks into combat, whereas the old 25mm ones i can only get one.
lets say there is a squad of 5 termis, vs 30 orks, on 25mm base i could fit maybe 6 into base combat (theoretically) whereas with with 40mm i could fit 12. having 12 in base contact means more will be within the 2" to be able to fight. and when ork boys charge at 4attacks each, you could imagine the difference it can make.
The only thing I can remember is that you have to use the base provided with Current models.