Of course there is not such a thing as best - this would imply it makes everyone happy, which is impossible to do unfortunately.
First - figure out if you want a hosted solution or a cart on your own site. Usually on your own site is better because you have a bit more control over it. You can usually easily move it to another hosting company if something were to happen.
Then determine what language you would like and what database.
Then figure out what all you would like to offer (i.e. real time shipping, what taxes to charge, affiliates, etc) and see what carts might be able to offer those add-ins.
Start with an already existing inexpesive shopping cart. I would say USD200.00 is good enough to start.
Look for simple basic functions like credi card processing, stock management, etc.
I advice you not to try to get the most complete shopping cart that will allow you look like Amazon.com as you will end up using only the basic functions at first. Remember that Amazon has millions of customers and they do need all those gadgets, add ons, and tools, but you probably will start with less than 20 customers, and won't need all those tools.