It is a dilemma isn't it?
If it was a small independent vets which has come recommended, then I would consider that one. A friend of mine, whose dog has recently had to undergo lots of treatment, was having to use 3 different vets - her own, from a PAH

who didn't have the expertise or equipment to do some of the treatment, which the other 2 local vets had. So it was all shared between them, for the best outcome of her dog.
Personally I prefer the old school type of vets rather than the more commercial ones that seem to come and go.
A spay is a very routine operation, so why not ask some other questions eg. are the stitches internal, therefore no need for a lampshade? Do you want to stay with her until she has had her pre-med? (I wish I had done this with Jinley) Does the cost include any painkillers and follow up visits?
I am sure others can give other questions to ask, which I haven't mentioned.