The M is far more machine. But that does not make it better. Big doesn't always fit the needs.
They are both Kubota top of the line models. Very difficult to say one is better than the other when you are comparing different size machines. Just because they both have the same HP does not put them to where they are really comparable.
Now for your own requirements, there can be a day and night difference, but you didn't want to put that on the table, so to be able to list out pros and cons properly is really about impossible IMO.
Good luck.