I use the bugle only during the rut and then to locate bulls. If you are good enough, they will at least answer you, giving away their general location. However, I have not had any come toward me, only take their cows away in response to my bugles, so I use the cow call in close to entice them in.

So the full answer to your question is take both if you are going during the rut, but use the bugle sparingly, and get some tapes of live animals and practice mimicing their sounds.