Both my children were born in the Summer (my son was born just at the end of Spring but it was hot already).
I would say Summer is the best time to have a baby. It's nice weather to take out the stroller & you don't have to bundle up the baby so much.
I actually was able to choose the time my kids were born (not an easy thing to do but easy for me). My company, as most, was very slow in the Summer. It just relieved some of my anxiety about missing so much work. I was the only artist at my company so I was able to make things a little easier for them.
This is just my opinion. If you have any good stories about when your babies were born I would love to hear them.
Have a great & safe Summer.