Agreed !! Magento is The most advanced E Commerce solution that can be compared to no other E Commerce Script , Consider the following things if you want to get into Magento: 1:By default Magento loads slow, Hosting can be bit costly 2:Simple extensions are Priced at $100+ 3:Customization again costs huge I wont suggest Moving to Magento unless Yours store do pretty ok money!!
Yes I agree with others that we cant compare both. Both virtuemart and magento are good on their own place as well as very powerful.
Magento is not simply a good alternative, it is much more... Yes it is a resource eater, but why don't you get a cheap dedicated server ? For instance I'm using popular deutch company called "Hetzner" as my dedicated server provider. They list their old servers for auction and these servers start from just 19 euro/month... Even the cheapest one will suit your needs with Magento. My personal opinion and advice is to start with a Magento immediately, don't waste your time with these solutions like virtuemart, prestashop etc etc...
[FONT=Arial, sans-serif]Magento is an eCommerce platform, while Virtue Mart is an eCommerce addition to a CMS (keep in mind the possible glitches in Joomla!).[/FONT]
I do really like Magento. I like its nice well thought UX design. Though it doesn't really differ from Shopify, Big Commerce and other builders. By the way, it's quite expensive. You can also check out some free builders like Tilda or Mobirise, in the case, if you want to create some small landing page.