I used Square (www.squareup.com
) at an event recently--super easy to use there, and I was told it was easy to set up, but I didn't actually do the set up myself. I think it's good for a one time event where you have to swipe cards, but it's not what you would use if you want to accept credit cards on your website.
I've used PayPal with three different organizations, and had some issues with it, primarily because we needed to have a webmaster with some programming knowledge set it up on the site; not just any joe could go in and set it up. And all three organizations have had issues where people think they have paid for and purchased something, when, in fact, the transaction has not been completed.
At my school we are using www.Pay4SchoolStuffOnline.com,
which works well for us. The fees are a little on the high side, but it's very user friendly and doesn't require any kind of programming knowledge to get it working.