I think Sept or October would be best but I am a teacher and tend to think of it in age of starting school terms! My 1st daughter is 3rd Nov. which i thought was good as its not too close to Christmas and good for starting school but its not according to her! She thinks its far too close to Christmas (bear in mind her poor sister who is Dec 17th!) and wishes her birthday was in June (shes ungrateful LOL) Poor DD#2 was born 8 days before Christmas in Darwin so it was hot and very humid and she never got to wear anything but a singlet until we moved back to Sydney in March the following year.
I must say I loved having a winter baby but the school thing is a pain as I don't know whether to send him young or late (he's 20th May).
DH is Sept 20th and it seems to the best time to me. Mine is mid january and its too close to Christmas and even though the sales are on half the time there's no money left after Christmas to buy me a present