I think it depends on what kind of articulation you're looking for... Im guessing you're talking about the high gain kind... a Plexi/JMP with a boost is pretty freakin' articulate IMO, but so is the VHT UL I played. The Diezels Ive played have been really articulate but I agree with Ejecta, they can sound a little compressed on some channels. Peter Diezel was actually telling me at NAMM he wants to take out some of the compression out of the 4th channel of the VH4 and third channel of the Herbert. Even he thought there was a bit too much.
I kind of felt like the Einstein was a bit too compressed when I played it at the Vigier bash, but I also didnt even bother setting it up, I just plugged in and said "fuck it, lets rock."
I think some of the Splawns are a bit comrpessed sounding, but when you come from a Non Master Volume amp into a high gain amp, they all sound compressed in comparison. And I dont mean that negatively. They're just different.