You can now set default payment types per customer by going to Edit Customer, scrolling to the Notes box and entering one of the following:
[PAY-CASH] = Default to Cash payment type for new quotes
[PAY-CARD] = Default to Card payment type for new quotes
[PAY-BACS] = Default to BACS payment type for new quotes
[PAY-ACCOUNT] = Default to Account payment type for new quotes (only works when paired with Account Type: Account)