Don't go with the cheapest you can find, try to get recommendations from people who have claimed. We went with the cheapest(Asda) about 3 years ago when we tried to claim they were useless, didn't answer emails or letters. We gave up on the claim in the end.
They have since changed their underinsurers so can't comment on their service now.
We have gone with Insure & Go they offer different levels of cover, we have gone for top cover(black) £130 for year family cover, cheapest was about £65. Hope they are OK if we have to claim.