You obviously have to use what best suits you, but don't forget that with less expensive-appearing services you typically have to pay 3.5-4% in processing fees, but they end up costing you far more when you factor in software development costs, merchant fees, and especially the amount of time you will spend if using an existing basic service that appears to cost less.

You also have to factor in chargeback fees, processing for non-qualified transactions (i.e. corporate cards, rewards cards, int'l cards, Amex cards, all of which cost far more than the often quoted 2-2.5% "qualified" transactions.

Thanks.