I would recommend Magento - easy to maintain and manage with plenty of extensions available and is also seo friendly.
I strongly recommend interspire shopping cart. It's user friendly and all the functionalities that I need for my ecommerce site is here. you can try the demo here iscexperts.com/viewtopic.php?f=2&t=2081
I believe here we must look through client's perspectives! I haven't find my clients happier than any other platform but Magento!
Thanks Everyone for their replies. It is sounding like Magneto is ruling the world in eCommerce Platform.
BigCommerce is a great hosted solution. If to choose between open source carts than PrestaShop, it is more user-friendly than Magento but at the same time offers almost the same functionality.
I was actually surpised to see Magento tied with OsCommerce. I used OsCommerce as a ecommerce solution from 2004-2007 and it worked perfectly for me, I guess I've been out of the game for a while and Magento has caught up!