Pretty much every big payment processor is viable so long as you have a US Bank account into which you withdraw your sales revenue—except a lot of us live outside of Bushland and thus the only option is either using a local bank/merchant account (expensive, complex, slow-moving, don't understand new technology, poor interface, etc) or paypal.

ApparentSoft is a developer based in Israel, like me. They probably opted to use PayPal because PayPal recently opened up the ability to withdraw directly to an Israeli Bank account -- something which all the ohter entrants on this list cannot do (with the possible exception of 2CO, haven't looked at them).

Most CC processors are much more expensive if you're only dealing with a small number of sales, they're only worth using if you're beyond a certain size which most mISVs won't be.

I've never understood what's the difference between a credit card processor and a merchant account? I've read up on them but I'm new to this and still don't really see what I should be looking for.

What about best alternatives for merchants outside of the US/Europe?