The SD-2 Pedal sounds much fatter and dirty I readed your post somewhere else I think that FD-2 or TS-9 will be your best choice
I had a chance play the TS9 and Boss SD-2 in a guitar store. (Please correct me if I,m wrong)I find that TS9 has a very clean distortion but lact of sustain, And with SD-2, there both distortion and sustain. I havn't had any chance to try Fulldrive2 yet, so I don't know how the sustain of that padel. By the way, I think effects are just like clothes. You have to try them on to see if they really fit your need. Sometimes when you find a good distortion effect with differet color in tones and you maybe buy it eventhough you've already had a dozen of pedal at home! So guys, next time before you complaint to your girlfriend buying too many new clothes, think about yourselves! Ha! Ha! Ha! Ha!...Sorry for a little bit long...
To Sun, You are absolutely correct that you should try and compare pedals with the same set up (I mean guitars and amps) thoroughly to see which one suits your need. Sometimes the difference is so subtle that you might ignore it due to various reasons (tireness, environment, etc.). My idea about the FD II is that it does provide much fatter tone simply because it boosts the mid and at the same time depress the high frequency. The downside of doing it is that it "colors" the tone a bit. It also sacrifices the "transparency" as well. I would not say which is good or bad beacsue tone is very personal. I even feel that tone somehow means personality. Mike Fuller (the owner and designer of Fulltone pedals) perfers the fat tone by overly boosting the mid frequency. If you listen to his music downloaded from his website (www.fulltone.com), you will immediately understand why. I do not think that there is anything worng with it. I personally perfer FD II over the Boss overdrive or distortion pedals because of two reasons: fatness and true bypass. Anyway, this is just my personal opinion for your reference. I still strongly recommend that try both of them with your own guitars and same amp in the music store; and be patient and thorough. After all, paying almost US$200.00 for a pedal is actually a big investment.