Keyword domain - better with dashes or not

Striclty from an SEO perspective, I starting a new website and have a domain name that consists of three words. The three words are a common search phrase and is exactly what my site is about. I have the domain name both with dashes, as well as without:
http: //www.keyword1-keyword2-keyword3.com
and
http: //keyword1keyword2keyword3.com

All three words together are 15 letters total... (www.123456789012345.com)... so not to huge (They are all about 5 letter words). There is no confusion about where one word ends and another begins, except one word ends in age... so you could wonder if it is another word (age) but if you looked at it that way the first word would not form another by breaking it there. I plan to do a 301 redirect for the domain name that I do not target as the main... My question is dash or not to dash the main domain?

Main concern is SEO optimization, rankings...

 

Unless the search engines can extract "unintended" keywords from your domain, you'll be fine with the non-hyphenated version. A good example of "unintended" keywords would be "Expert Sex Change" - which would come from expertsexchange.com - that's why Experts Exchange has the hyphen in their domain name - experts-exchange.com - to tell the search engines that THOSE are the only two keywords they should pay any attention to.

If you can't do that with your domain, you'll be fine without the hyphens.