What are the pro's/cons of each?
One pro for caps is that they are cheaper! The AVR ditty for my unit would cost another near-$400. The pro for AVR is, presumably, much tighter voltage regulation with load.
But mebbe AVR has its limits ito ruggedness?
The voltage swing on my genset is 250 - 230 V, 0-50 A. Units with AVR claim 1-2% regulation.
Should I spring for the AVR? If a major outtage occurs, I'll be running cnc equpment from it.