MCH is fairly fast paced due to its Hypercharge rapidfire combo - 1.5 GCD + Alternate between Heat Blasts + Gauss Round + Richocet. The other skills are much slower in comparison -Heavy Hitting GCD attacks, but because the speed at which you recharge Gauss Round and Richocet in the later levels is much faster and you can stack to 3 charges per skill, it becomes much more fast paced feel because you're consistently using oGCDs for a more sustained momentum. It's a bit on the slow side, but a lot faster because of the oGCD feel.

NIN has a 2 sec GCD so they're naturally a lot faster, but they burst windows have a huge APM increase because of how much skills / damage goes into their Trick Attack Window.

MNK is slow at first, but it ramps up speed with more stacks of Greased Lightning. Now as a passive trait, your GCD is extremely low at higher levels, so you're constantly attacking real fast. It doesn't have much oGCDs, but rather requires you to nail every positional within the lower GCD to do high damage.