Do you really care?
Seriously, I liked the first 2-3 albums pretty well, but after that...
I was always a BS&T man myself. Liked their horn writing more, even if David Clayton-Thomas' vocals were kinda creepy and the image of Dick Halligan scoring w/groupies is even creepier. Still, other than James Pankow, I think BS&T had "better" musicians, although Bobby Colomby vs Danny Seraphine probably comes down to a matter of taste.
I mentioned this elsewhere, but it bears repeating. The influence of producer James William Guercio on the early Chicago sound cannot be underestimated. If you doubt that, listen to two Buckinghams albums he produced, TIME AND CHARGES & PORTRAITS. There's a shitload full of moments in those albums where you'll swear you're listening to a Chicago album.