I have a September baby (well.. She's almost 4) and fall was PERFECT to have a newborn. Sleepers to dress her, cool enough for baby wearing and learning to nurse.
Summer 7-9 months pregnant sucked though.
I also have a January baby, and she was 6-8 months her first summer. Kind of nice because she could sit and crawl.
We are thinking of a third and I have no idea when I want to "try" next year!