What's the best way to build quads? Either the leg press or hack squat with ascending and/or descending reps. Each machine removes the required stabilization associated with barbell squats. The possibility of losing your balance is gone, so you're free to focus all your energy on quad contraction.
Yes, I believe instability techniques can activate more muscle fibers, but I've seen the most growth when I can harness the mind-muscle connection with heavy weight. Some favor lighter weight and high reps for quad development, while others opt for max effort low-rep schemes. I do believe in the metabolic hormone cascade which follows a very high rep (20-30) set of hacks or presses on occasion, but exclusively high rep sets failed to bring me the greatest gains.
Low reps (5-8) have always given me the best results, but the risk of injury increases substantially when moving maximum pounds. Thankfully, I've got a solution which harnesses the benefits of both high and low reps. Most serious lifters are familiar with drop sets, but few of them do ascending sets.
Then, without rest, add just one plate to one side and do 5 more reps.
Again with rest, add one more plate for another 5 reps.
Repeat the one-plate addition two more times. You'll end up with 8 plates per side. In the end you'll have done 25 total reps via 5-reps bouts with brief pauses while a training partner adds plates.
You get the pump and the hormonal cascade as you would with a high rep, low weight set, but your last bout of 5 reps is likely a little less weight than a max effort, low rep set due to the accumulated fatigue which mitigates safety concerns.
If you're really adventurous, you can actually do both ascending and descending in one set, like this hack squat workout:
Note: To achieve overall leg development (not just quads) nothing beats the conventional barbell squat with a medium foot placement.