I don't think a mix of Bb and G would be a good idea. One of the main goals of having a good hornline is blending together, having one sound. Putting Bb horns and G bugles on the same field would be like trying to mix water with oil. Bb horns have all (or most) of the volume of the bugles, but the quality, tone, intonation, etc are so much better!
My opinion: Bb, or be flat!! ........