The OP was specifically asking about what’s best for SEO. Though as they say “What’s good for the goose is good for the gander”, translating to what’s best for human visitors is generally best for SEO too.
But when words are bunched together into one, the resulting string may not be an actual word. Spiders may be able to detect words with such a string, but there may be some ambiguity to what words exist, or where one starts and another begins. The classic example being www.expertsexchange.com
Google has said it does see hyphens as spaces, so in breaking the words you are clearly defining the two keywords that can be found in a dictionary.
From a human point of view, I think it reads easier. Though I think it could get awkward with a greater number of words.
But as already stated, this is a minor factor, Google is far more interested in the keywords within your content, not your domain name, so I would not lose any sleep over it or spend too much time deliberating over it. Use the name you think looks best and is more memorable and easy to read.
If you do want to spend more time on this and hear more opinions, it has been discussed before with pros and cons for both sides.