I'd appreciate your advice for getting the cheapest car rental, picking up and returning to Heathrow for 13 days in May. I can't get a straight answer from anyone I've talked to on how much of a discount I'd get if I joined a company like AARP or AAA, bought an Entertainment Happenings Book, or used a certain credit card like American Express, etc. I just want to make sure the membership/book cost warrants the savings. Another major frustration I have is there's 4 adults and 4 pieces of luggage (not sure if all will be considered large) and each car rental agency has different descriptions for the luggage that will fit, often on the same car so I don't know who to believe. I'd prefer not to rent a full-size if a mid-size will work but I don't want to get stuck with not having enough room for our luggage. Thanks for your help.