To follow or nofollow?

For external links what is better? Rel=nofollow or follow? I've had follow there since I installed vbseo just wondering if it should be a no follow instead.

nofollow is always better for it and you must implement the same there.

I recommend following everything, and use the blacklist to nofollow certain sites.

Why is that. I thought nofollow for external links would be better on forums with spam etc. I know it can't be used for forums that advertise as some advertisers don't allow nofollows on their links, but what about forums that don't have external advertising?