Can't agree more with the comments from Shopaholic, specifically on the Nationwide cards.
The "Best Buy" by far is the Nationwide Flex Account Debit Card. No charges at all, - even for ATm's - and this makes it unique. Also a better exchange rate when you do use it, even in an ATM. However, it is a Debit card not a Credit card, so you will need to settle your bill every month. One way to get around this is to "pre-load" your account with the total you think you will spend or pre-load it on a monthly basis. The fact that you are going away for 7 months means that you will have to be a very organised/disciplined person.
I have been a Nationwide Debit card holder for some years and cannot speak too highly of it, having used it in Europe and Australia.