You really would benefit from all of it in order to have a diverse backlink portfolio, but the most powerful links pound for pound are in-content links on High PR sites that are related to your niche. But shoot, I'll take one regardless of the niche it's from, those are powerful links. Here is some research info for ya... http://www.seomoz.org/blog/17-ways-search-engines-judge-the-value-of-a-link
I agree, in content links are probably the most powerful. High quality low quantity links on high PR pages are good also.
But I think the general consensus is that a good mixture is the recipe for success as it will look the most natural.
When it comes to linkbuilding, everything works the best equally.
I want to know which is best among all those?
directory submission is very difficult,most need exchange the link.bad.i think directory submission is best