I do a lot of range work with many calibers and would like to ask you experts what 9mm Glock is the best for continuous target practice?

Recoil is of no concern, but having a good trigger is.

How does the 17L compare to the 34 and which is best?

I think the 17L is a great pistol, however I dont care for that long of a barrel (6.02 inches). I think the 34 aims and feels better. I have shot some IDPA and steel plates with the 34, its a very fast gun, easy to make follow up shots. Just so you know the barrel length on the 34 is 5.32 inches. After I shot the 34 I liked it so much I went out and bought a model 35, which is the same except in 40 S & W, I only went to the .40 for competition reasons. Hope tihs helps.