Intonation better on Bb's? Overall yes, but its just as easy to blow out of tune.
Listen to the end of 2004 Cavies. That mello note about 10 seconds from the end blows so flat it hurts.
I personally feel that a G line should get demand points because it's harder to keep them in tune. It can be done tho. :)
And, 2000 Cavies were on G bugles.
If you wanna hear Bb's and G's playing nice together, listen to the combined Caballeros (Bb) and Caballeros Alumni (G) play Flamenco Cha-Cha (or is it Cha-Cha Flamenco? :P). Granted, a number of people will hold the 3rd valve on the Bb's, but others don't, and its still an awesome sound.