Depending on the style you're looking for, I still recommend the Metal Zone. Great sustain for a pedal.
Most of the others mentioned (Rat, DS-1, TubeScreamer) work best when pushing the first gain stage of a tube amp. Thus, if you are runing them into a tube amp, they should sound great. If you're not, they won't sound as sweet.
If you're gonna rock, go for the Metal Zone.
Most importantly, go to the store and play a few pedals next to each other using YOUR guitar and preferably YOUR amp. Take what we said as a platform and then make the decision yourself based on your desired tone and playing style.