I have done both clinic spays and hospital spays. It seems just the luck of the draw, but the only cat I lost and the only cat to get sick were both done at the veterinary clinic. I don't blame the vets that did the surgery, sometimes things just happen. But, I would not avoid a clinic out of fear either.
I have only felt once that it was definitely the right decision at the right time. That was a dog that was very injured in a two on one dog attack. The last one, I definitely waited too long. It was only a week, but what a horrible thing to put an animal I loved through. The decision is personal, difficult, and many times does not feel right. We do our best and love the next one that purrs or wags into our life.
I just hope you find peace when the time comes to make the decision for your current furry friend.