For people who've seen my posts over the years, it's no surprise that sax quartet is my major focus. It's the instrument I play, and I get to play and hear my own pieces performed. I like the relatively consistent sound of the instrument from top to bottom for each individual horn, and across the group's combined range. There are nuances of course, especially in the bari's upper range, but having that consistency has helped me focus on the structure and style of the composition by taking "color differences" out of the variable mix.
I've also written for up to 8 saxes, and that's really not that much different because all it adds is the possibility of "thickness" and not new colors.
From there, however, I'm branching out to full concert band.