Go for Warwick. Theres no difference between Warwick and Imperial. They're both so extremely strong, except, Imperial is in Central London which is why it is more known around the world. Obviously, it's in London- a part of the top 5 cities.
I do Maths at Cambridge. When i was applying, it was hard to choose Warwick or Imperial as my insurance especially because the offers were the same. I chose Warwick at the time because their maths course is so fantastic. Imperials is just pure, hardly any chances of getting any nice applied mods, such as Physics. At Warwick, under strict circumstances, it is easier to obtain mods that you are stunned by, obviously having the pure mods as core and the applied mods as optional. It was so much better for me. But to be honest, everyone I know here had insured Warwick, UCL, Durham or Imperial for literally every course. (Mainly Warwick and UCL), so wherever you go, you'll find it great.
Good luck. You have fantastic offers to deal with.