Ahh the infamous "distortion pedal?" question. Asking which distortion pedal is best is like asking a group of individuals their preferred ice cream flavor. You're going to get alot of different responses. A better question would be "What kind of distortion should I get to do ______. (insert purpose here). If you want a good Dave tone which I assume you do since you're in this forum, the Big Muff is a good place to start, which alot of people have mentioned. Also, the Boss Blues Driver is another good choice. I picked up a Boss GT-3, the first GT effects unit they ever made and I must say, I can pretty much nail the tone on the PULSE version of "Sorrow" and "Run Like Hell" using that unit's delay/compression and a Danelectro Daddy-O. One thing to remember about effects processors is DO NOT use their distortion because it ALWAYS is bad. (My experiences anyways)

Another important thing is the amp -- tube definitely required. A Marshall and anything that uses a similar circuitry *ALOT of amps* break up really easily. Dave uses Hiwatt amps which are notorious for having a low break tolerance. Matchless is another amp with this characteristic. I play through a Traynor Mark II head, which is basically a Marshall Super Lead 100 circuit and I get close to his tone despite the tendency for it to overdrive.

With any blues based guitarist I think the most important thing when trying to replicate them is do your own thing and get the point across. Dave never plays the same solo twice so why should you try to play his exact solo? If you break into "Comfortably Numb" at a bar and you rip out a sweet solo and it's not exactly the way he played it, who cares. No one is going to call you on it and if they do, they better prove themselves as a superior guitarist

The hard thing about pinning down a Dave tone is that his tone changed throughout the years. You almost have to pick a decade of his music and go from there. I prefer the Delicate Sound Of Thunder/PULSE tour tone so that's what I shoot for.

-Taylor