I wouldn't do anything in a Smith machine personally, but agree with proper atg squats, with slight pause at bottom.I'll take a set of 20 reps at 135 lbs. done ass-to-grass.
I always do my squats via the Smith machine, and, as part of a 6-set series, I never exceed 225 lbs. for 10 reps.
For me, the key is DEPTH (whether done via the Smith or free weights). I've seen many knuckleheads loading the bar to 315 lbs. and squatting very half-assedly.
Lift a lot less weight compared to when just about hitting parallel so a bit of an ego check needed initially.
Makes me laugh to myself when men banter about how they squat 140kg plus for 8 reps. In my experience very few men get near parallel when squatting any weight, never mind average looking men claiming big figures. Every couple of inches of depth makes a big difference to the weight yiu can move without sacrificing depth.
Yeah you get the odd powerlifter/strength focused trainer who does, by they are a tiny % of the population. Even bigger impressive looking chaps (lean and muscular and there's a chance they're using gear anyway... fair play if they're natty) moving bigger weight rarely go parallel.
Plus going atg with lower weight carries less risk than wobbling around with big weights you can't reach parallel with.