I prefer with forum...

I agree, some blog comments can be worth it. Otherwise it is so much faster to do good work in Forums. Most blogs you come across have Nofollow backlinks and usually don't even like backlinks if they are public and require no registration. And i don't want to spend several minutes registering to make a comment that could possibly be removed. So I mostly hang in the forums.
If i see a blog with a high PR and dofollow links in the comments, sure I'll register :D :D