Hams, seem to be easier. It is probably the way i do my exercises. For example always, do full squats, never parrallel or partials. Same with Leg press like to put my feet high up, get a good strech, feel i use my whole legs that way but maybe more so my hams. To me it's just less stress on my knees that way. Plus as mike mentioned lifts like stiff leg deadlifts working the hams.
For me I have to beat and beat the quads for them to grow, but hams always get a good pump and burn and they just seem to get bigger.
I have really big biceps and triceps are a pain to get big, legs seem to follow this idea ,big ham's and pain in the ass quads.
Now, if anyone figures out the secret to a giant back that is what I really need...
