Rental Car Pre-Authorisations/Deposits and/or Best Company to Use?

I am going to be visiting the UK for three weeks in August/September and am need to rent a car for a portion of my trip. My current thought is to pick up in Maidstone on 31 August and drop off at London Gatwick on 14 September so I realize that I may end up with a one-way drop fee however the part that I am really finding confusing is the amount of money that will be held against my credit card as a pre-authorisation. Under the Terms & Conditions for Europcar, it states that £250.00 will be held except in cases of "all first time customers who present a foreign driving licence and have a UK address will be required to pay a deposit of £1000.00." I assume that would apply to me as I have not rented with them before? Other companies seem to have a smaller hold from what I can tell in reading the fine print but does anyone have any suggestions as to which is the best car hire company as far as price and customer service goes? I have rented a car in the UK once before with Enterprise (2015) as well as in Ireland with Hertz (2016) so would I be better off using one of those companies instead of Europcar even though I can get a better deal with them?