We are with Animal Friends..... We haven't had any problems with them as such but you do have to read the small print carefully!
There have been a couple of occasions where they have not paid the full amount of the claim but when queried, it is always because of something correct that I had missed in the small print if that makes sense!
MIL is with Buddies pet insurance and her elderly dog has had many health problems over the years. She has never had any problems with them and her vet claims directly from the insurance company. However, they are more expensive.
As we have 4 dogs insured, we do have to keep an eye on the cost and as mentioned, we have not had any problems with Animal Friends.