I like the sd-1 more too, like friendship, I think asymmetry sounds a little grittier and overall cooler. If I was getting a tubescreamer I'd just buy the cheapest most readily available clone (you can get the digitech one at jb-hifi for 70 dollarydoos or something), I think they're all pretty damn similar - tightens the bass and bumps the mids.
They're pretty boring but indispensable for anything chuggy using amp distortion. I don't like how they stack into a rat/muff but maybe other people have had success using them with other pedals.