Good question Dognott! I personally would suggest a glass call. I say that because with a glass call you can actually manipulate the glass with different grit sand paper. On one of my glass calls, I have sanded 3 different areas of the surface for 3 different sounds. For this very reason I don't care for the aluminum calls. The aluminum already has its own grain, so you pretty much just get whatever sound the particular grain is. With glass, if you don't like the sound or doesn't seem quite right, you can change it at any time.
Hope this helps! Good luck this year! [:)]
"The doorway to freedom is framed in muskets" Charleton Heston