On an SEO point of view they are both pretty much the same. Some people say that domains with dashes are harder to rank since they are commonly used by spammers but I think it is a myth and shouldn't make any difference. I always recommend without dashes so it is easier to remember.
I agree w/ seosapien on all points... I think they rank equally as well. However, when picking domains I always go after the one without the dashes. But when picking names of pages/folders for that domain I always separate keywords in the page/folder name with hyphen. So for domains I pick domains like: www.keyword1keyword2keyword3.tld because you want people to remember your domain and for it to be easier to type. But for pages/folders I pick page/folder names like: www.example.com/keyword1-keyword2-keyword3/ www.example.com/folder/keyword1-keyword2-keyword3.html because people are less likely to remember complete paths to pages on your sites. So it's less important to make them easier to remember, and here I worry more about making it easier for the engines to find my keywords in the page/folder names.
Domain name with or without dashes will have same SEO value (if there is any difference that's too low to be noticed). I will encourage you to go with domains without dashes because they can spread by word of mouth.
it is important to have your main keyword on the domain. its hard these days to get a domian name with one or monre words for any major TLDs. if you can get the domain name with dashe, then go grab it. depends on how you use your domain also. if you more care about branding, then a domain without dash will work better. if SEO is of more importance than branding, then dash will work fine