Someone has to be cheapest....
I would personally check -
Customer Care
Legal Cover
Hire Car etc if needed
Modifications if you have any or plan any
Protected No Claims i.e. vandalism etc
At the end of the day they are a business so they have to cut costs somewhere...
I never go with the cheapest quote until I check everything it's a bit like buying beans in the supermarket you get Heinz at 99p, own brand at 49p or value at 19p anyone that says they all taste the same is