Flying into LHR in Sept., will need a car for two weeks. What company has the best value....2 passengers, 2 lg bags, would like auto trans. Thanks
Use a search website such as kayak.com to look for vehicles. Also check directly with the usual companies like Hertz, Avis, National, etc. to see if discounts are offered for AAA and other memberships. Last Spring I found the best deal at Hertz, surprisingly, which on top of a good deal was charging only £1/day more for an automatic. I normally won't pay extra for an automatic, but in that case I did. My navigator appreciated the smoother shifting.
Autoeurope( a broker that handles all of the Big Boys) has a sale going on now. Check them out. Note that if you pick up a car at any place other than the airport ,it is usually much cheaper. (fiddle with their pick-up and -of locations on their website.) Make sure that you understand how much deductable you will have for theft and collision. If you buy/cover this "excess" at the rental office it can cost you up to $20/day extra. Look at Thomas Cook, etc. for cheap "excess insurance".
We've done well with Auto Europe. Based in the US, they connect you with a choice of rental companies and plans. They sometimes offer free GPS with advance rentals, very useful to have. A good credit card may provide enough insurance to save you the cost of "excess" coverage, though a claim would be more complicated. Check your card's benefit details. BTW I hope you're not planning to drive in London as the title of your post implies. Excellent mass transit is much better than costly driving and parking.