According to your own experience, which credit card processor would be both the best reliable and affordable?

It all depends what you're looking for: Lowest price or best service.

which credit card processor would be both the best reliable and affordable

I'd highly recommend getting a merchant account. PaySystems.com offers these, as well as 3rd party processing services.

The way I look at it, ifyou're starting out and want to save costs, you can go with a cheaper service a la 2checkout.com, and switch to a quality provider once you start getting business.