Yamaha Amp comparisons?

This question is for those who may have owned various Yamaha amps at the same time and switched them in and out of their system. If you were able to actually compare them side by side what were your thoughts about the following. I will divide it into classes /eras as that may help. I have owned a few but not at the same time and know the sound did change. With the idea that gear ones own sonic preferences can make a big difference what is the best sounding units from the list below? Family traits? Thanks

M4 M2
M60 M80
M65 M85
MX 800 MX 1000
MX 1 MX 2