Tube Screamer is a nice round mild overdrive, used a lot as a booster placed before another distortion source, but "mild" is the keyword here. I'd go for DS-1, because of its harder distortion and more trebles. It also acts well when reducing the level on the guitar (That's the way I use it, no on/off switching). The last time I used DS-2 was ages ago, but I don't remember liking it, mainly because DS-1 has much more usefull tone control.