I'm dealing with a Magento 1.4.0.0 Community Edition installation with various undocumented changes to the core (mostly integration with an ERP system), an outdated Sweet Tooth Points & Rewards module and some custom payment providers. It also doubles as a mediocre blogging/CMS system. It has one store each for 3 different languages, with about 40 product categories for a few hundred products.

[rant] With no prior experience with any PHP e-commerce systems, I find it very difficult to work with. I attempted to install Magento 1.4.0.0 on my local WAMP dev machine, it installs fine, but the main page or search do not show any products no matter what I do in the backend admin panel. I don't know what's wrong with it, and whatever information I googled is either too old or too new from Magento 1.4.

Later I'm given FTP access to the testing server, which neither my manager or I have permission to install XDebug on, as apparantly it runs on the same server as the production server (yikes). Trying to learn how Magento works is torture. I spent a week trying to add some fields into the Onepage Checkout before giving up and went to work on something else. The template system, just like the rest of Magento, is a bloated mishmash of overcomplicated directory structures, weird config xml files and EAV databases. I went into 6 different models and several content blocks in the backend just to change what the front page looks like.

With little-to-none helpful and clear documentation (unlike CodeIgniter) and various breaking changes between minor point revisions which makes it hard to find useful information, Magento 1.4 is a developer killer. [/rant]

The client is planning to redesign the site and has decided it might as well as move on from this unsustainable, hacky, upgrade-unfriendly, developer-unfriendly mess. Magento 1.4 is starting to show its age, with Magento 1.7 coming soon, the client is considering upgrading to Magento 1.6 or 1.7 if it has improved from 1.4. The customizations done to the current Magento 1.4 installation will have to be redone, and a new license for the Sweet Tooth Points & Rewards module will have to be bought.

The client is also open to other e-commerce systems. I've looked at OpenCart and it seems to be quite developer friendly with a fairly simple structure. I found some complaints regarding its performance when the shop has thousands of categories or products, but this is not an issue with the current number of products my client has. It seems to be solid ground for easy customization to bring the rewards system and ERP integration over.

What should the client upgrade to in this case?