Summed up: quick and simple is best.

I might add that if you’re not trying to build your own self-hosted customer base, using a well-known point of sale like eBay, Amazon, or iTunes, or a highly-used, 3rd-party checkout option like PayPal or Google will create much less friction than a home-brewed option. Granted, your per-item profit margin may decrease, but so would tech support and website maintenance. Not to mention, with less friction sales are likely to increase enough to make up for that lost profit margin. (Via Marco.)

How to Achieve Painless Registration