I am a huge fan of carbon fiber, my bike is carbon and the spokes on my wheels are carbon; but, there are somethings that just don't need to be made from carbon--stems and seat post are such things. Unless there is some substantial weight savings, I am fine with aluminum.

What I look for in a stem is the length and angle that works for me. The clamping mechanism will not crush my bars and the weight is reasonable. I have always used Ritchey but I would use others brands.