Sorry to hear your dog had an accident.
The age may well be an issue.
I used to work in the business and I think 8 was the cut off for some companies not to give insurance to new customers with dogs that age.
They do vary considerably in price, but of course, the more you pay the more cover you get etc etc. And remember that although there are loads of "brands" of pet insurance (all the supermarkets, M&S and loads of others do it) the actual insurance company behind all these is often the same.. Just with different fronts on them. So the service you get for say, M&S and Sainsburys pet insurance is all from the same centres with the same processes.
I have only had to use my policy once and I must say, it was handled quickly. I am insured direct with AXA, who back a load of the famous name pet insurance schemes.
Not a big claim, though, so they just settled up. Larger claims will attract a lot of scrutiny and in those cases the good and bad payers will become more evident!
Can your vet recommend who they like/get the money from quickest? They may have a relationship with a particular insurer (but beware that this isn't also particularly more expensive)
I think you can have good and bad experiences with any insurer, it's a bit of a lottery TBH.