I posted a post like this a few months ago (I'm afraid I do not know the link to it) and the overall concensus was the NFU - I think KBIS was in the middle, then Petplan then E&L etc.
Another vote for Amtrust. Lightening fast payment of claims and friendly knowledgeable staff. Very impressed with them.
Interestingly I was chatting to my vet and he asked who I was insured with (poor Amtrust, another claim shortly coming their way). I said don't worry its not E&L and he said they have got a lot better recently. Apparently they have new management and have changed their policy, so now they are putting their prices up but actually paying claims, instead of trying to wriggle out of them. Still, I wouldn't risk it, I'm very happy where I am and who is to say their policy won't change again!
I did use Petplan, and when I put in a huge claim when Mazzie was killed they did pay, although it took a while and they wanted more information including proof of ownership (shouldn't they have asked for that when I insured her?!)... However they get you with the renewal... For Genie it went up 13%. I voted with my feet and am now with NFU.
NFU paid out no problem with Felix and were very helpful. But they loaded my policy on my next horse as I had made claims before, even though it's a completely different horse - as though I was the risk! Didn't think that was fair.