In reply to GStone:
I've hired cars for a group of 4 every year for the past 10 years or so. If available at a sensible price, I normally go for an estate - an Octavia is perfect, but the smaller estates, such as Renault Megane and Ford Focus, are generally fine. Otherwise, any intermediate-size car should be ok. I've never tried one but I would say the C-Max looks ideal.
I usually book through www.rentalcars.com. The prices are usually quite good and they allow you to book up front and just pay a deposit.
I agree with the advice that you should take out separate excess insurance (available online for as little as £2/day). We were hit with a bill for £250 last summer for a tiny scratch on the hire car. The insurance company paid up without question.