You should also consider length as well. I just started using dpn and bought some 5" and 6" that I'm using for Caps to the Capital for baby caps that are 9-11" finished diameter.
I knit continental and find that the 5" irritate/dig into the meaty part of my palm below my thumb. The 6 inchers don't. I also prefer bambo over wood (ie Brittany) in the larger size #5-#9, but okay for size #1 & #2.