About a year ago I played around with Agora and was impressed – until about 6 months ago I played around with OSCommerce and was even more impressed.
The only problem I had with either was that I did not need all that power; therefore, I opened an account with third party credit card processor. (2checkout instead of Agora and then a merchant account at Paypal – then I made 'order' pages and check out pages with links to these third party payment processor's. Both of these third party companies have 'merchant accounts' - with built in shopping carts. So I use the shopping carts from third party merchant accounts - and let them worry about the SSL
As far as the two shopping carts, I 'sorta' remember that Agora was tricky to set up and did not have as many features as OSCommerce. But then again – I never really needed to add the merchant accounts so I'm not sure how easy/hard that would be to do with either of these.
But since I like to 'guess' – I think a person would need a lot of products (a small online Wal-Mart business) to justify the learning curve of using either of the shopping carts. And then my 'best guess' would be to use OSCommerce – I used their support forum and it's full of helpful people IMHO.
Just my 0.02¢: