I've been using 2checkout for many years, dropped them about 2-3 years ago because of hidden fees. Basically if you sell and get paid in currency other than USD, they charge extra 10% for currency conversion.
So customer pays you in EUR, money is converted to USD, 2co gets their fees, then when you withdraw money it converts back to EUR. However those conversion rates are different - one for buying USD, one for selling USD. Difference is about 10%. It doesn't show up anywhere on website, I had to find out hard way after losing many hundreds.
PayPal doesn't do that. If customer pays in EUR, it stays in EUR account, then withdrawn in EUR as well. No unnecessary conversion.
But otherwise 2co was good. Problems arise only if you are not in US and get paid in anything other than US. They also had slightly higher fees than PayPal.