I have a good list of edu links, i am thinking to build only edu links, is this good or page rank or not?
I cannot really understand ur question ? It is not bad to create only edu links , You should create backlinks from all categories sites !
You can go to any Blog, Forum, Directories etc. and comment thus you can place your link in there. But don't spam around; instead your comment should be valuable and should be useful for readers in there.
Of course they are good but are they related to your site? Having them related/in the same market is obviously going to be a lot better than just links from random .edu sites.
.edu links are really effective but you should also create links from other sources otherwise only .edu links will look as spam to search engines.
You should focus more on high quality/PR links than focusing only on EDU. The majority of EDU links you'll get are from over-spammed comments and xrumered forum profiles, nothing of real value and easy to identify from Google's side.