I say Box Squat or PL squat as your ME exercise.
I don't like GM's as a ME exercise cause I tend to overpower my hamstrings and use my lower back which is strong enough. But using it with lighter loads and higher reps (ie, 6-8) it is a GREAT assistance exercise for me and has greatly brought up my hammies.
In your case between the two exercises i'd choose Good mornings, i feel RDL's hit it a bit more...
GHR is THE exercise for hamstrings, if you can even try practicing the manual one's its something at least (and hell of a feat of strength).
Another exercise I like is Snatch Deadlifts off of a box... recruit's posterior chain and hip flexors like CRAZY cause you're ridiculously deep.