Which is better for SEO? A domain named “http://www.besttennislessons.com” or “http://www.best-tennis-lessons.com”?
Short and dirty answer is: Which ever one is better for your visitors to read.
So, do you think your visitors would better click and respond to the domain without hypens? or with the hypens? That’s really up to you to decide. Having the main keywords you wish to rank for in the domain name is a very good tip. So, if your site is about “tennis lessons” and/or you want to rank highly in search engines for those words, then having them in the domain name is a very good place to start.
Always try to get a .com, .net or .org domain if possible. As always, if you want to know if a domain is taken just type it in directly or use http://whois.net to get the registration information.