I like cherry, it gives a nice deep red color to the skin. Apple is also good. Both are mild and don't overpower the turkey. I just use 2-3 small chunks. Pecan might be a bit too strong for my taste.
I used pecan this year, 2 medium and 1 small chunks. Flavor was good but a little on the lite side. Used 2 big chunks of apple last year, very tasty and many compliments.
I am doing chicken this afternoon. I normally use apple since I have an orchard. I have never tried cherry but can easily rustle some up. I've got a lot of white & red oak, hickory and some cherry.