I went from a 2012 Speedmaster (air-cooled, EFI, 865 cc) to a 2017 T120, and there is no comparison. Everything is better on the T120: the brakes, the power, the torque, the feel on the highway, 6th gear, suspension, just about anything you can think of.
This is kinda like comparing apples to oranges, though, as I never rode an air-cooled Bonnie.
I guess a lot of people miss the 360 crank of the air-cooled models. That does not apply to me, though, as I am pretty sure that my Speedmaster, while having the same engine as the Bonnies, had a 270 crank to make it sound like a cruiser.