I have a gear drive in the form of the M6060 and an HST in the form of the MX6000. If I ever had to part with one tractor it would be the MX and I honestly feel that I wouldn't miss the HST much at all. Driving into a dirt pile isn't any trouble at all with the M, and the hydraulic shuttle is kind of awesome, but they are very different animals and mastering the M is just a matter of seat time.
The only bothersome thing about the M is the "need" to keep the revs up for the DPF to avoid excessive regen cycles, and high revs and the shuttle don' t play well together. I'm still learning how to use the clutch pedal, the shuttle, the hand throttle, the accelerator and engine rpm in the best way possible, but as I said, it's just seat time.
I have a Jeep TJ with a 5-speed manual transmission, and my F250 is automatic. I like the variety, and feel the same way about the MX and M. I enjoy the different driving, handling, operation and capabilities of those two machines. I don't plan on parting with either and hope I never have to, but if the MX6000 with cab had been available in a gear drive model I would have chosen that over the HST.