I think slate makes the best soft purrs, clucks, and tree yelps and is the easiest to run. If you want volume, go with glass or crystal. Glass/crystal is easy to run too, and you can make some really nice turkey music with them. My favorite running surface is crystal. The Primos Power Crystal has been my go to call for the last couple of seasons. To me, aluminum is the hardest of the pot call surfaces to use, but some days it drives the gobblers just bonkers. I find it hard to purr on an aluminum call, but maybe thats just the one I have or maybe its just me? I have called birds in with aluminum from verylong distances though. One more surface you might want to consider is the sla-tek synthetic type. It sounds pretty good and is very easy to run. Knight and Hale's Ol' Yeller uses this and is an awesome call for a beginner. Hope this helps.