The actual anaesthetic used is far, far less important than the experience of the vet in using that technique. Injectable anaesthetics are much more widely used in Britain compared to America, and many vets are not equipped with Isoflurane but use Halothane instead. Halothane is fine if the vet is experienced at using it. You need a vet whom you trust to do the best for your rabbit. Of course you must also be willing to pay the appropriate rate - at least the same as consultation fees as dogs or cats and in some cases more.
Expertise can be very expensive.
Access Taking your rabbit a long distance for routine surgery or second opinions is fine - few of us are lucky enough to have an expert in the same town. If your own vet is not a totally rabbit whizz-kid, fine. I would much rather see a vet willing to treat my bunny as the beloved friend he is, who will use the books and seek advice when he doesn't know, than someone who doesn't like admitting their limitations. Etiquette Your bunny is a patient of your vet. It is very, very important to respect that relationship with your vet.