Hi Gina,
We normally recommend OpenCart unless you have specific needs. It's modern, lightweight, and easy to use.
Otherwise Magento is popular and does offer functionality that OpenCart doesn't. If you have a particular need for that functionality or will be running a very large online shop, then Magento can be worth considering. It is notoriously resource intensive however.
PrestaShop looks great out of the box, but is less customisable and lightweight than OpenCart. It probably sits somewhere between OpenCart and Magento in terms of its weight.
WordPress + WooCommerce is also a popular choice for less traditional eCommerce stores - such as ones with just a few items that you really want to show off. It's very simply to use and looks great.
Any decent web host will provide a one click installer so you can install all these platforms in seconds and have a play to see which fits your needs best.
Here's the website of the one we use, which provides reviews and demo's of the popular options:
https://www.softaculous.com/apps/ecommerce
We also summarise 10 of the most popular eCommerce stores, under
eCommerce Software on our website.
RomanCart isn't actually provided through Softaculous.
Personally I'd stick with the more popular open source platforms.
RomanCart appears to be more of an add on to an existing website to provide eCommerce functionality. So a store integration.
As
@Food From Cyprus said, if you're starting from scratch I'd probably look at the more popular options.
If you have any questions feel free to get in touch.
I hope that helps.
Best of luck,
Dan