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)