I'm wondering the same thing...
Obviously You won't find in opencart forum people saying "virtuemart is better than Opencart" isn'it?
But I'm trying to compare features..
this are Virtuemart features (I changed font color for those I don't find in opencart features)
* capable of using Secure Sockets Layer (https) Encryption (128-bit)
* flexible Tax Models
o Model 1: ShipTo Address-based Tax Calculation
o Model 2: Store Address-based Tax Calculation
o Model 3: EU Mode (Store Owner based Tax Calculation when Customer comes from an EU Country)
* Shoppers can manage their User Accounts (registration required)
* Shipping Address Management (Customers can enter their own Shipping Addresses)
* Order History: Shopper can view all their previous Orders (and Order Details)
* Order Confirmation Mail (customizable!) is sent to Shopper and Store Owner
* Multiple Currencies (you can allow Customers to change the Currency and buy using an alternative Currency)
* Multiple Languages (using the Joomla! Component Joom!Fish or Nooku).
* Manages an unlimited Number of Products and Categories
* Can be used as a Shop or just as an Online-Catalog (you can even turn off Price Display)
* quick Search for Products, Categories and Manufacturers; filter by features or discounted Products
* Product Ratings & Testimonials (moderated or auto-published)
* feature specific Products by setting them "on special"
* Product Availability: show how fast a Customer can expect delivery
* Handles downloadable Products (virtual Goods)
* "Product is back in Stock"-Notification for subscribed Customers
* multiple Images and Files (like Spec Sheets and Flyers) per Product
* Product Attributes (like Size or Color) can be added to Product
* Product Types for Classification (like "Car", "Motorbike" or "Music Album")
* Shopper Groups for Customers (allows different Price Levels and Payment Options),
* multiple Prices per Product (Quantity-based and/or Shopper Group-based Prices)
* flexible Price Display (number & currency formatting; including or excluding tax)
* On-the-Fly Price Conversion between different Currencies using Live Rates from the ECB or other banks
* Shop Statistics / Control Panel with a Summary of new Customers, new Orders....
* Stock Level Control for Products and Item
* Order Management with Order History, Customer Notification and Order Edit Functionality
* basic Reporting Feature: sold Items, monthly/yearly Revenue
* Order Status Management
* manage different Currencies, Countries & States
* capable of live Credit Card Processing
* pre-defined Payment Gateways like authorize.net®, PayPal, 2Checkout, eWay, Worldpay, PayMate and NoChex
* extend your Shop with other Payment Modules using the Payment Module API!
* flexible Shipping Carriers and Rates Configuration
* Live-Shipping Rates using Shipping Modules (e.g. InterShipper, UPS, USPS, FedEx or Canada Post; Modules can use the Shipping Rate API).
* extend your Shop with other Shipping Modules using the Shipping Module API!