Just sell things, enough things that it actually matters who you are using for processing. But, with 0 sales, you are doing 0 order processing so it doesn't matter.
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.
That said, I'm moving off of them to a WP + WooCommerce shop this month to have better control over the process and offer something besides PayPal (several countries are blocked from PayPal).
I like the design. I like the simplicity. People can just use their CC like normal. They take a percentage of your sales, but so far found it worth it.
I wish it had order tracking (just a box I could tick when I shipped something would be nice) but that is irrelevant for downloads.
Pricing for Snappy Checkout is the same no matter how many tiers your item has. It's 2.9% plus $0.30 (for Stripe/PayPal) and 2% or $0.50 (whichever is less) for Snappy Checkout's fee.
If I did not answer your question, then please email me at Mike@SnappyCheckout.com with some more details.
Flat monthly fee. Their admin UI is clunky, their checkout pages are basic but functional, but they solve a number of problems* without asking for a percentage cut of sales.
I think for basic stuff they work just fine. I'm just selling one ebook and I just wasn't comfortable with having a cut of my sales taken AND my funds being withheld by a third party before some weekly or monthly remittance. With e-junkie the funds go straight to my PayPal account where I can use the money immediately (I constantly pay for things via PayPal).
*obfuscating download path, handling coupons, handling multiple downloads etc
Let's me sell a per year license with an optional reduced renewal fee at the end of the year, which most services don't seem to easily offer. Also then lets me ties into other things like support forum membership.
From their website (http://getdpd.com/plans-and-pricing/):
"What types of payment do you accept?
We accept Visa, Mastercard, and American Express. At this time we only accept payments online so we will not be able to accept a P.O., invoice you, or take an order over the phone."
It's bitcoin only though but I like the preview for music and the no-bullshit easy handling.