I've built these, all kinda marshall sounding
Wampler Plexi Drive
Zvex Box of Rock
Catalinbread DLS (not mk3)
HAO Rustdriver
MI Audio Crunchbox v.2
For me the Wampler PlexiDrive sounds the best. But it was a pain in the ass to try out those JFETS until I found the right ones (went through about 40).
The HAO rustdriver has a really nice vintage Marshall tone, but is not very versatile stock. I modded mine with a gainpot and a tonecontrol.
The Catalinbread DLS is very nice. It sounds very similar to the Box of Rock, but the DLS is thinner sounding and Box of rock a bit fatter with alittle bit more gain on tap. Generally I think that DLS for humbuckers and Box of Rock if using singlecoils.
The Crunchbox sounds awesome, but it's more of a modern hi gain marshall sound. If that's what you're looking for don't hesitate to build it!
I have yet to build the Carl Martin Plexitone and the Runoffgroove Thor (I love the ROG stuff!).
Cheers/ Fredrik
check out my building blog at www.parasitstudio.se