Comparing Prestashop , Opencart and Magento depends very much upon the user perspective . e.g
Prestashop and Opencart both shopping cart module are fairly lightweight as compared to magento with less table creation in database but from developer point of view Opencart lacks some of the very fundamentals features E.g
Observer Design Pattern – Opencart Does not Support Observer design pattern as magento does so for creating module in opencart is really a painful task when you need to extend the functionality of the module without affecting the core .
There are third party module and apps like VQMOD and Override engine but both of them are not good as magento is . so from developer point of view opencart lacks a lot of key design patterns and structure .
Factory Design Pattern – Unlike magento using opencart factory design pattern is really very painful and everytime you need to replace the core files unless you are not using third party modules like VQMOD
Loose MVC structure MVC and ORM structure of the opencart is not good as magento have .
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Marketplace for Developers – Opencart marketplace is way to Good as compared to prestashop . IN opencart everything is automatic and really a heaven for app developers
Prestashop marketplace is super slow everytime when you update your app they take weeks and month to update the app also they have very protective system no information about the developer in their marketplace .
At E-commerce and ERP Development we are dealing with prestashop , opencart and magento development regularly so all of framework have their own pros and cons .