It depends. If you are looking for comments and traffic on your site, open it up to do follow. If you are worried about PR, too many do follow may dilute your PR so try no follow.
Nofollow has no real SEO benefits in Google. SE bots don't count them as backlinks. However, they can still generate traffic to a site.
Why do follow gonna dilute your PR?? Isn't the case, the more quality do follow links that u get, the high PR you gonan get??
The PR juice not follow on no follow links, so no follow is not beneficial in case if you want to gain Page rank....... And do follow link are very beneficial as its help to gain the Page rank as well as the SERP.
do follow link is more better than no follow cause do follow link is raise to SERP & traffic but no follow only generate traffic.
Webmaster like dofollow site because it can provide PR juice. To set your own site to dofollow can attract more visitor but many of them are spammer, so make a choice. By the way, your PR wouldnt drop if you change your site from nofollow to dofollow
Looking at the context of the question, the thread starter was asking about having do follow or no follow on his/her site not links coming from other sites.
Your questions are not clear. I suspect you're asking about whether to make the links on your site dofollow or nofollow. But you need to clarify. In any case, here is something I wrote about dofollow/nofollow which should help answer your questions. I give reasons why you might choose dofollow, and reasons why you might go with nofollow.
If you get dofollow links that will help to get good PR as well as good traffic If you offer dofollow links, lots of spammers will come to your site and spam your site, so your PR will go down.
Do-follow is better for SEO, however, having No-Follow links isn't a bad thing as Google still "sees" those links, but doesn't give them weight. Be everywhere.
The "dofollow" attributes for external links dilute the PR as some part of a page's PR values goes to the external urls it points or hosts.