I installed magenta and love it and it is still in beta however not fluent enough with php so I am waiting for the stable release which will have additional themes. I cant wait for it to become stable. Impressive open source application! Os Commerce and Zen Cart will be dead.
If you want to run a download store then ezypal.com is your guy. That's what I use for my gamepacks.org site and it works very well. I like it because it's very flexible. You can add multiple files, configure multiple products for each file, categories, custom pages, etc. For example I sell a gamepack for multiple arcade scripts. Well the games and the thumbnails are the same. The only thing that changes is the sql dump file. I can use the same game and thumbnail files for each script. Only thing that I don't like about the ezypal.com is that support sucks. Actually I can pretty much claim there isn't any supported. You can ask a simple question and it takes days in not weeks to get a response. It's actually pretty cheap for the amount of features. It's only $24.95.
Which of these have a template engine? I have spent hours modifying the look of oscommerce and still so much to do. Then if I get away from it for a week or two I have to go back through all the code and relearn it all just to make changes. I would like to fine one that has a template system like wordpress or pligg.
I am currently designing Treadmill Reviews with Magento. It is not going to be an ecommerce site but a review site. Magento will dominate the open source ecommerce market. The program is very flexable. The only issue right now is finding a host that this program will work with. I have a dedicated server so I can control the configuration. One of the server requirments will be PHP 5.2
I don;t think Magento will become something powefull for ecomerce like wordpress is for blog.But who knows.... I suggest using anther script.