I am making a 3 tier baptism cake this weekend and they want the bottom round the middle square and the top round. I would normally do a 10,8,6 but when I stack the pans the middle square seems to come out too far on the bottom round. Should I do 12,8,6?
Go with what looks best for you.
Square cake on round one and round cake on square one work very different then both rounds or both square.
For my tiered cakes (not that I do so many of it) I make the "pan check" each time.
I would just go with whatever looks best. It's hard to say because I'm not there looking at the way the pans stack up.