Ease of use, Clean dashboard, constantly developing new releases and features, testing library, accessible pricing options.
The entire quality assurance process is pretty difficult with VWO, making edits to dynamic pages is nigh impossible out of the box. Customer support can be spotty. IMO the heat map functionality just doesn't work.
VWO isn't perfect, but it is a great tool if your organization is looking to get its feet wet with Conversion Rate Optimization. They are developing great tools and features, as well as providing a library of testing ideas and case studies in case you're having trouble thinking of what to test.
Their results reporting isn't iron-clad, but for many efforts it's good enough. I personally am not a big fan of how "confident" they are in their declaring winners - I've seen tests where one day it says a variation is a winner at 100% confidence, then the next day that's down to 81% (think about that for a second).
However, for most new testers, it's a great tool and definitely a lot easier to use than a tool like Google Optimize.
The price point is very reasonable as well, making it accessible to companies of all sizes.
VWO helps me test specific variations through their A/B testing platform as well as measure their results. It also works well as a "traffic splitter" to send traffic to different URLs, even if you bypass the editor.