At first I used the in-browser stylesheet and template editors Squarespace's free/low-cost plan had to offer. But almost immediately my clients had to step up to a plan that allowed me to access the Git-based developer platform. Unfortunately, they wanted to retain much of their existing markup and styling. It was all dependent on the system blocks johnny_utah mentioned, so I couldn't take the greenfield approach. This created some problems, but it still didn't take me long to put together a very nice brochureware site. And I am definitely no expert with the platform.
Yes, I would recommend Squarespace over WordPress. It seems very empowering to slightly-technical users who might want to do creative things that would be difficult with even a customized/fully-plugged-in WordPress setup. Also, avoiding WordPress security issues and third-party hosting headaches is a big plus.