My suggestion would be to 301 redirect the lesser of the two to the bigger one. That means if one is PR 3 and the other PR 4, redirect the 3 to the 4.

I can understand about wanting multiple domains, one with a hyphen (-) and one without, because Google looks at URL's. It sees a hyphenated domain as two separate keywords, such as "my-example". The other version looks at "myexample" as one word, that no one searces for. But those domains are still valuable too, after people remember the name of your site, they're more likely to type it in as the latter of the two.