I've gone through three or four routine changes over the past year, of course. Went from:
High touch-and-go box squats (about 20" stance width and letting the knees drift forward)
Trap bar hack squats
High box step-ups
Lying leg curls
Tried front squats for a while. One of my favorite quad movements, but my left knee won't tolerate them for very long.
Full-depth back squat (narrow stance)
Put almost 3" on my lower quad measurement and, sadly, dropped almost an inch from the upper measurement.
I have recently been introduced to chain and band work. Reverse-band full squats with the EFS Short silver bands takes off ~180lbs on the way down, so I can really load the top of the movement without sacrificing depth. Each rep is a struggle from beginning to end, and it's awesome. Can't wait to see the results in about six months