Wich one should I inorporate to my hamstring training? Wich one is more effective in glute/ham development?
RDL's are the way to go. It is easier to keep good form with them versus SDL's when you start to fatigue during your training session. It is easier to squeeze the hamstrings and glutes with this exercise from my personal experience.
I don't actually do a SLDL. I also don't actually do a RDL.
What I do is a hybrid of the two. The movement at the hips and lower back is similar to the RDL, in that you maintain an arch in the lower back and lower until you reach a stretch in the hammys. It is like a SLDL in that the knees are only slightly bent and don't bend further during the movement.
The reasons for this are that a slight knee bend will hit the hamstrings more than a larger bend or a movement of the knee. Keeping the lower back from rounding should be obvious (well except to Chewie ).