I may well be e-junkie's oldest surviving customer, although I eventually transitioned everything off their app into my app with the exception of Paypal IPN processing. They've got almost $500 of LTV from me, $5 a month at a time.

If I were making the choice again today, it would be Gumroad by a country mile. Regardless of whether you end up using them, look up Ryan Delk's presentations regarding the habits of successful sellers (multi-tier products; X 2.2X 5X pricing; email marketing). They'll make you much more successful than the typical person who just throws a $FOO onto the Internet.