I had missed twice with my girl doing vaginal AIs. Once with progesterones done and semen looked great, next time just followed my boy's instinct. So we did a surgical AI next time around - got 4 pups. She just had her 2nd litter - did one progestrone to get a rough idea where she was in her cycle. and then did 3 vaginal AIs - one every other day. The result was 8 puppies.
Another girl, I did a vaginal and a surgical AI since FedEx dropped the ball on delivering the goods and I drove to the stud owner's home, we did a vaginal and then followed up the next day with a surgical. Got 10 puppies. Her next litter was a vaginal AI - once every other day for a total of 3 AIs - one progesterone to get an idea where she was in her cycle. The result was 9 puppies.
I believe there is a time and place for a surgical, especially if using frozen semen or if you have had a girl that has missed more than once. But with my second girl, I feel that I got talked into the surgical by my vet.
We do surgical AI's on almost all breedings. We have found it to be the best method for us to insure pregnancy. Our repro vet typically does them 72hrs after ovulation (5ng progesterone). The litter sizes have typically been in the 6-8 puppy range on average. We have done one back to back on a bitch that was ready to retire upon the advice of our vet.