I registered with BMTMicro and it was easy to setup. They also provide custom layouts and can pay you both by wiretransfer and paypal. I will know once I start selling (hopefully soon)
I agree that BMT have the best Customer Service around. Their one problem is that they do not have some of the features and customization of Plimus....sure you can contact them and get them to set it up on their end, but I always liked how Plimus handled bundling, promotions, etc.
Be sure to take a look at FastSpring as well. You've never experienced this type of customer service as a game developer.
FastSpring works with various gamers like: Studio Eres (Immortal Defense) Nifflas (Saira) Distractionware (VVVVVV) PomPom games (Astro Tripper) hermitgames (Leave Home) Alastair John Jack (Arvoesine) Arcen Games (AI War) Ludosity Interactive (Bob Came In Pieces) Data Realms (Cortex Command) Backyard Ninja Design (The Great White Destroyer)
Stripe.com is by far the best in my opinion. It's so simple to install, the documentation is incredibly clear and useful, and you don't need a payment gateway!
Stripe is fantastic, I set up free PrestaShop on jetpackhq.com, so total costs are $45/year for a dedicated ip + ssl, plus 3%-4% total for Stripe fees. Compare that to 10%-15% for services like BMT. I have my own key generation system and user database. I would prefer to let an outside service handle support & shipping etc, but I can't justify the price difference.
Stripe is fantastic because its API system. If you have the developers for it a Stripe powered billing/key system can be exceptionally powerful. Its transaction fees are similar to PayPal but unlike PayPal its other misc fees (AmEx, Chargeback, Refunds, International Cards, etc.) are much lower. I haven't had deal with customer service so I can't speak for that but I think anyone is better at PayPal. That being said while it doesn't have an API like Stripe I did have some experience with Amazon Payments through Kickstarter and I didn't really have any complaints beyond the arduous verification system.
We have used Big Commerce. Its a US based platform but really good for the complete novice as we were/still are. Lots of online advise, videos etc.