I don't know if the gap is closing but Visa was previously advertised as being more widely accepted in Europe whereas Mastercard was the preferred option in America
Depending on the bank, the repayment system can be different. As with most credit cards, the visa requires you to repay the minimum amount each month. Most mastercards do too, but AIB used to offer one where the minimum payment was set by the credit limit, not what you owed. Pros and cons there.