Depending on the complexity required, I often use Wix for small-to-medium businesses to build their websites.
The main reason is that I can create something unique from scratch with no templates, and because of the incredible - and free - functionality available.
The only downside is the higher hosting cost but this is offset by the fact that clients can update the sites themselves and not have to pay someone to do it; and I can design a beautiful site more cheaply (and faster) in the first place; so lower upfront costs for the client.
We at Bondi Websites DO utilise wordpress, Joomla and other platforms depending on the needs of the client; but SEO is NOT platform dependent so has nothing to do with my advise to clients.
Many developers pooh pooh wix for its SEO; in the past this has been an issue but this information is now out of date due to the huge amount of work Wix has done to fix those issues.
Here is a great article by another Wix Pro in Victoria which discusses (with some lovely strong language) the old wix vs. wordpress debate.