Clearly Magento, and if you don't agree then there's something seriously wrong with you.. or you've never checked it out (pss it's free).
osCommerce is severely outdated and is a nightmare for anyone new to it who plans to make modifications or fix bugs themselves. The latest release was in 2002 I believe? CRE does a decent job with updating / bug fixing if you want to pay for it though. Zencart in my opinion practically follows my same opinion of osCommerce. Magento was very nice at its early stages for numerous reasons, but it annoys me that they stripped so many features from the community edition to try to upsell their commercial edition. Opencart seems to be pretty nice, I haven't spent too much time with it, but after a quick glance of the file structure it is something I will be looking into in the near future. Edit: I see a lot of people like AJ cart. I see they offer their Developer edition for $2000 and I would strongly advise caution with their expensive products. Several years ago, I hired them for a pretty extensive project which they required up front payment for. I had to wire the money overseas and waited patiently for the final product. After 4 months, they sent me their "finished" solution which was not anywhere near to working. Two months of email / phone and many "updates" for their code and I gave up. Their terms of service clearly stated that there was a no refunds policy not even partial refunds. I was informed that this still applies even if their product doesn't even work.... I understand that things change and this company may have got it's act together, but I still urge caution with them.
so, one can have an e commerce site without having a fresh script and design ? Are these ready 2 use stuff secure ?
i would definatly say opencart. it is so simply to use a 3 year old could manage it! I tried using oscommerce but it's just not up to standard and their are never new versions of it whereas opencart there is a new version nearly every month! so my vote is for opencart hands down