I dont know wheather this question is asked before or not..I am thinking of having a website which lets users to share notes and lab work of univeristy, so am thinking of having it in the form of forum, am planning to use some free bulletin board, i heard mybb, phpbb n SMP are good once..But am still worndering which of these is better compared to others..some say mybb is better while others say phpbb..please suggest me :)

Why don't you install a local server and install them? That way you can try them and see which one best matches your wants/needs.

Apart from that, SMF is my personal favourite.