If you had the ability to choose between Magento, Miva, osC, ZenCart - which would you choose. Each one, by my reckoning has great value and I am having issues deciding which to use. Here are the comments collected from Internet and you would be able to make decisions based on these:
Magento: graphically pleasing, multiple stores in one store, ajax, easy to customize
Magento is very graphically pleasing, but don't just jump in because of the pretty backend. Magento is still very young, but if you are comfortable with the OOP approach and specifically the Zend Framework setup that they have, Magento could turn out to be a great cart for you.
Magneto is slower than an oscommerce site, loaded with products. And that's very slow. Its why the trend back in 2005 was to go with CSS/XHTML php carts like Zen cart, instead of table based carts like Osc.
Magneto is nice in the way that web based flash applications are nice- it is packed full of great features that run like a snail unless you spend a fortune on specialized web hosting.
Also, the template is inflexible in critical ways, such as altering the nav bar to be a side menu instead of a top nav bar. There are also some key bugs in the bulk-uploader (if you like to manage stock via a spreadsheet)
it's not really ready for the mainstream yet. It IS bulky and slow, and pretty much requires a dedicated server to run (you don't even want to try it in a shared hosting environment). The real WTF moment for me was dealing with their templating system, and the fact that all their add to cart/checkout buttons won't work AT ALL with javascript disabled.
As of the current Magento release, more products == exponentially slower performance, especially while searching the product catalog.
The good news is that the development progress on it seems very active, and they will no doubt address the (huge) performance concerns at some point in time. And when they DO solve those performance problems (and other little "gotchas" like javascript issues), the software will be almost unbeatable.
Miva: very robust and well documented
Miva is very robust, but FAR from well documented. Recently purchased, the new owners (who were actually the former owners) claim that this will be fixed soon. While the community is very active, every modification you want to make will cost you $20-$100.
osC: great support community, somewhat easy to design around, user friendly
osC is dieing. Version 3 has been "in progress" forever now, and Magento has really tried to replace osC as the #1 open source cart.
Zen: same as osC but better with features and easier to use
Zen is a pretty good cart and is still very active. The infrastructure is similar to osC, but very different than Magento's. Zen relies on "hacks" more than "addons", which can be very, very messy.
In summary, don't stand miva. It's expensive and has very little support, and hard to modify (the hardest). OsCommerce has died, they are more concerned about fighting than getting anything done. It's been over 3 years that 3.0 is coming. Zen is just a knock-off of osCommerce and has no future without osCommerce.
Magento is backed by a commercial company who has an interest in keeping it new and fresh. I feel comfortable believing that these few items (yes performance is bad) will be addressed soon and I'd rather be able to upgrade a Magento store then have to upgrade from another to Magento.
