I design, build and maintain Squarespace websites. As a proud member of Squarespace Circle, I've created several highly effective websites (including my own), and provide maintenance for numerous others.
Easily Customized Templates: Squarespace offers lots of beautiful, functional templates that are ALL FREE (and safe since they all come directly from Squarespace, rather than a third party as with WordPress).
No Need for Plug-ins: Squarespace features, such as mobile-ready sites, commerce tools, blogs, image galleries, podcasting, etc., are all built-in (unlike WordPress which requires you to download plug-ins and hope they are safe and won't eventually break).
All-in-One: With Squarespace, all of the technology is managed for you, so unlike WordPress, there's no need to deal with backing up or updating your site, or paying for a third party host.
Top-notch Support: Squarespace Support is available 24/7 via email or chat, and during business hours via phone. This is not an option with WordPress, where you'll need to sort through forums in hopes of finding answers.
Lower Cost: Squarespace websites cost less than WordPress sites once you add in the various costs of reputable themes, backup and security plug-ins, feature plug-ins, hosting, etc.