Recommendation: The Park SW series of nipple wrenches should be in every bikers tool kit. I have them all, but you should definitely have the size that fits your bike(s). I've seen folks say that they easily strip your nipples. Just take your time and you'll be fine. Any wrench can do that if you're not careful or are dealing with rusty or parts filled with crud.
Recommendation: Park makes two version of this spoke wrench, as will all sizes. The SW-0 is the 2 sided wrench where as the SW-40 is the 4 sided version. I would recommend also springing for the 4 sided to take better care of those soft nipples.