What you may consider a great impulse may be considered shit to another. There are no ideal impulses. Even an ideal impulse may sound like shit on a terrible amp sim, same vice versa. With that being said, some of the most respected impulses on here are catharsis impulses , asem recto v3 l2, orange_2_mics, guitarhack, fredman, gods cabs, Clark Kent Match EQ IR Collection. Or do what a lot of are starting to do, create your own match impulse using Clark Kent's Guide. http://www.ultimatemetal.com/forum/production-tips/710368-yt-match-eq-ir-tutorial.html
What?
To use ir's you want to have a di track going through an amp sim to the ir. OR record your amp through the fx loop fx send and hit it with an ir.
If you mic your amp and put it through a ir youre recording guitar like xzibit and get weird boomines.