For 250-300 watts and up, use PWM...
Class H requires a larger heatsink, larger power supply (much more "stout")
PWM much more efficient.
They both preform equally well, but PWM wins out at high power for ease of construction etc...
Well, I see Steve has chimed in while I'm typing this.....
My PWM is in a 3RU (5" high) 12" deep , 17" wide (inside space) box.
That's power supply and all. WITH a transformer
It's good for approx 320 watts out to the RF deck.. Limited by my too-small toroid power transformer,,, could be 400-450 with a bigger one in there...
With Steve's new "Easy-H", The modulator/power supply, AND a class-E RF output stage for about 120-200 watts will EASILY fit in a box the same size as my modulator alone.
Though maybe needs to be a 4RU box, just due to the heatsink mounted board's "circumference" with devices installed, and the height of the inexpensive power transformer that Steve has made available....
Haven't actually built one YET, because I don't have a board