If you are using PayPal I would strongly recommend using Payments Pro. The Payments Pro option lets users enter credit card details directly on your site on the checkout page as well as click on a button to pay with PayPal. Payments Pro consists of Direct Pay (credit card) and Express Checkout (pay with PayPal) together so that your user has a choice.
If Payments Pro is not an option for you I think Express Checkout would be second best. I would not recommend using Payments Standard, it can be very difficult to get working correctly and does not provide the best user experience.