I've been using Magento for the past year and half. Out of the box, it's rather striped down and basic and although you can purchase a lot of 3rd party modules from their Magento Connect store, the cost to get the cart where you wan tit, can begin to add up quickly. I know WooCommerce, which is a cart built for Wordpress, is setup the same way. I can honestly say between testing my company with multiple carts before I found one I was happy with, I spent a great deal of money on customization and modules.
It really comes down to what sort of store you operate. Each cart has their profs and cons and limitations. For instance, my store needs product options such as drop downs choices and text fields. Cs-Cart is an example of a cart that has that capability built in at entry level, whereas Magento requires me to buy a separate module that was like $100+. If I didn't need that, maybe Magento would have been a better value. On the flip side, I also needed the ability to support multiple store views which CS-Cart can do but at like $150 additional per store view, whereas Magento offers unlimited added store views at no additional charge.
I still like the way Magento functions and find the platform rather stable. I don't think the back-end is as well laid out as CS-Cart as far as quickly accessing customer information and order details, but much better laid out than WooCommerce IMHO.
In my experience, finding a good cart comes down to coming to terms with what you need from the cart, and what cart can achieve that the closest. Obviously, you may need some additional modules here or there, but the more changes and customization you implement, in my opinion, the great chance the whole thing comes crashing down as some of the changes may conflict with each other.
I love CS Cart and use it for all our sites. It's supported and they have a team of 150+ developers. Magento is far bigger and has a massive community BUT... you need an experienced developer team to run the community edition. I find the interface also far better on CS Cart and I believe the learning curve on Magento is steep.
I m definetely sure that Magento is the best cms platform. Magento can easily handle any big number of products and customers and allow you to expand further in the future if necesary. There are a lot of benefits in using Magento platform, too many to count in one short message. It has a very enhanced system for managing the products, clients, billing, mobile shopping and so on. It has a lot of features for cross-selling, up-selling, special offers and other tools for marketing. It is the most used e-commerce platform all over the world (more than 25% of the entire market) Magento received a lot of rewards, but most importantly It has powered most of the 1000 Top Best Internet Retailers in the last 3 years. Magento is the leading open source e-commerce platform in the world, so it would certainly be a good choice.