I think the answer to the question is not relevant because it creates this all or nothing scenario which is not realistic for most of us with families, mortgages, etc.
I would qualify my answers (just to be different
) and say if I had to just have one of the three: M3 hand down. But if money was not an object and I could have two of three it would be M3 and M6 GC. And lastly, I would never own all three M couples or sedans. I would replace the M5 with X5M instead or replaced the M3 with a Porsche 911 S. Then again maybe go with the Ferrari 458 or maybe,,,,,,,,,,,,,
Money changes everything.