Wait till after first heat
I am a believer/supporter in the wait till after FIRST heat or Batch of puppies. They are more mature and I've seen less health issues associated with it. Larger breeds do tend to go into their first heat later around the 8 to 12 month range so you have time. The closer to the heat cycle the better if you can't wait.
IMO the reason for this trend of fixing early is a reflection more of convenience and population control. Similar to the C-section trends it seems in human births nowadays. 10 years ago, vets weren't so insistent with recommending the fixing of the animals as they are nowadays. Maybe it's due to advances in medicines or population levels are out of control. Either way, I am sticking with waiting till the appropriate time.
Scooby, Shaggy the "Dogs", Ms. Thang the "Cat" and introducing Measley Weasle "The Ferret".