hi wayne and welcome to WebmasterWorld
the *best* option for an ecommerce site is the option that is most suited to the needs of the site, not the cheapest option, not the most expensive option, but the most suitable option regardless of cost. get it right first time and you'll (hopefully) make good money and save yourself a lot of hassle in the future.
look at each catalog / cart / card processing system you find and determine which of them will do what the client needs from day one. some will have extra features the client might want in 6 months time - it could be a major headache to change everything in 6 or 12 months time so get it right from the start.
eventually you'll have a short list of catalogue / cart / card processing options to present to the client with some costs. next enquiry you get you'll have a fairly good idea of what they need etc.
you can find a lot more information about catalogues, carts, card processing systems and everything else to do with ecommerce in the ecommerce forum at
take your time and read back through old threads - there is a lot of very valuable information there.