Choose a County Court near to yourself so you don't have to travel too far. Also makes it more difficult for the defending party to attend the court.
By default you can have the case heard in a court nearest to your address, you don't have to choose the court at the outset. In fact you can now lodge a small claims court case online (Northampton handle this, but move to your local County Court for any hearing). Full details at
www.moneyclaim.gov.uk