Just like with tires, most brands of brake pads come in a variety of formulations (models). Depending on your needs, any particular brake pad may be great or terrible.
For example, like docjohn, I have had a bad experience using Porterfield R4S pads at the track (the backing plates softened enough to fold around the caliper piston
). But those pads are okay for everyday street driving. As he notes, Porterfield also makes track-only pads, the R4; those who use them generally like them a lot.
The same thing can be said for pads from Cobalt Friction, Hawk, Carbotech, etc; all these brands make some pads that are designed for everything from street driving to track use only. Track pads tend to have more grip and more resistance to fade at high temperatures; the downside is that they tend to squeal and dust, and need to warm up to be fully effective.
Right now I'm really enjoying the Cobalt Friction GT Sport brake pads; they're great for my needs. I use them on the street and on the track; they just barely squeak on the street (almost none) but they grip nicely on the track and last as long as most other pads. But those who switch pads for track use are more likely to love the Cobalt Friction Spec VR pads, which generally get rave reviews from the diehard track folks.