Have a search on eurocarparts. they often have promotions on, currently its 15% off batteries
i recently bought an Exide. I didnt have any specific preference on the brand, i dont think there is a great deal of difference between them from my experience, but often you get a 3 year warranty version or a 4 year warranty version. i went for the longer warranty because it cost less than £10 more and if the battery were to fail in that 4th year it would cost me more than £10 to replace it