All other things equal, which is the most effective URL?

In the eyes of a search engine..

[harleyx]

As far as search engine optimization and URL rewriting goes, I see three major types:

1) h..p://www.example.com/keywords.html
2) h..p://www.example.com/keywords/
3) h..p://keywords.example.com/

All other things being equal, what is your opinion of the most highly valued URL among those three in a search engine's eyes?

I use the 2nd one currently and it does well, however I'm thinking about switching over to using the 3rd type as it seems to do slightly better - though it's hard to tell because "all things being equal" is almost never the case.

What do you think?

[blue_eagle]

keywords.example.com should be better if other things equal.