Then do both.
Utilize light weight but high rep leg curls and extensions to warm up effectively without tiring you out. Then do your squats/leg press so you are warmed up but still fresh. Finish with heavy weight isolation work such as leg extensions. I personally like to work my hams before squats too (heavy) as this doesn't usually interfere too much with my squat (feels good). I have to add I don't squat heavy to much now due to back issues but that's what I have done in the past.
I change the order most workouts but something like that below is always good. Just adding a rough ideas of weight used but things like drops sets can be used with great effectiveness.
Leg Extension- Light
Lying Leg Curl- Light
Hip Work- Light to Moderate
Seated Leg Curl- Light to very heavy
Squat/Leg Press- Light to very heavy
Leg Extension- Heavy
Lunges- Changes... as much as you can go... usually light as can barely walk at this point.