Which way is better and why?

[Oppenheimer Group]

The name used as a string, I assume, performs better due to the proximity of the keywords. No space, no punctuation.

When doing searches you'll often find inferior sites, both in links and optimization, but highly ranked because they are a direct match to the search terms.

[ResaleBroker]

It is my understanding that Google ignores the hyphens in the URL in regards to "exact" search terms.

[Oppenheimer Group]

Hyphens are fine for page names. And for that matter for the domain name. However, my experience tells me the non-hyphenated name will out perform the hyphenated version.