There's so many things I like about Miva the company, and Miva Merchant the product.
Technical Support: Miva's support team is awesome! When I call in, I immediately get a person. When I create a support ticket, I usually get a response within a day. They also have a very active forum where you can also find help or get tips or news.
The Miva Merchant software is equally amazing.
Fast: Because Miva is written in MivaScript and it's compiled, a Miva Merchant storefront loads quickly. Other shopping cart software I've used in the past, or recently reviewed, is written in php or some other non-compiled language, so it's not so quick to load in your browser.
Flexible: I've used several e-commerce systems over my now 20 years of building websites, and Miva Merchant is the most flexible I've seen. I've never had a Miva developer turn a request of mine down because it couldn't be done. I can't say that about other e-commerce platforms.
Themes: Miva, Inc. has built some themes that are ready for use. They range from very simple in design to fully-loaded designs. And they're FREE! The themes are easy to install and customize.
Features: I've never seen a more flexibly set of features in a shopping cart software. When I say Miva Merchant comes with 'coupons', that's not doing the software justice. You can do a lot with Miva Merchant's coupons feature.
More: The folks at Miva, Inc. are constantly working on new features. I always looks forward to what they're working on next.
A recent set of problems Miva has solved for a client of mine:
A particular clients previous site was slow to load, was not flexible, was stuck thinking within the previous systems limited set of options. Every time my client asked me to do something with their old e-commerce system, I had to tell him I couldn't or it would cost thousands of dollars.