This is really just a question of practicality since both result in a record of monies paid out on behalf of the company by an individual which should be reimbursed at some point.
Generally where supplier invoices come into the company it might be easier to process these as normal and where an individual is paying these personally then select the appropriate Director’s Loan (bank) account when posting the payment to the application, whereas when an individual is out and about on company business, paying many small bills as he or she goes, then these should be claimed formally from the company at the end of each week or month via the Expense Claims procedure.
Posting the repayment of a Director’s Loan (bank) account is achieved by a Bank Transfer to that account from the bank current account; posting the payment of an Expense Claim is processed through New Employee Payment (see also How do I claim Expenses? and Which Bank Account do I use?).