This is purely subjective. Even on this site, which is purely subjective, this is double subjective. But you asked.
I think SquareSpace is the best choice for the beginner. Its feature set is limited, and its interface can be frustrating to learn. However, its tools work well, and it’s possible to create a decent looking site without any HTML or CSS knowledge. Moreover, it’s hard to screw up too badly. Even a poorly constructed site will work.
Wix is easier to learn, but it creates sloppier websites. I’ve never had somebody show me a Wix site without apologizing for it first.
WordPress is the most powerful platform, but the hardest to learn. Most amateurs buy a theme, and then stick to the theme’s framework to build their first site. However, that framework may fit awkwardly around the edges, which is why so many first-time WordPress sites look like a teenage boy wearing their dad’s suit. I love WordPress, but to get the most out of it, you really need Web development skills.