Tweed, Mark I, and Mark IIC+ on triode, thas what i have been using, but i have not experimented that much with other modes, the other day recorded a guy in Edge and it sounded awesome, he recorded with a dual terror and the Mark V edge, some great tones over there, and sometimes i use mark IV or Extreme for metal chunks or detuned stuff.
The only mode I don't really use is Clean. I probably just need to spend some time with it. But once I heard Tweed on 10w (and 45w), I pretty much stay there for channel 1. Like most, I spend the majority of time in Crunch and Mark IV. But what I love about the amp is that once I have had something dialed in for a while and starts to get a little stale, I just flip to a different mode and start exploring again.
I guess it's a toss-up between Tweed and Mark IV. There are just so many good things going on between those two.
On channel 1 I use Clean mode because it's articulate, stays clean and doesn't get boomy with heavier picking on open chords. On channel 2 I use edge for lesser gain rhythms, it has a great high end shimmer and is extremely dynamic and responsive to my picking. I actually use it for leads with a tube screamer thrown in front. On channel 3 I use the extreme setting for heavy riffing, I stay here most of the time. I love how aggressive it can get with out getting saturated, it's extremely transparent. I like this setting the most, it definitely achieves "the sound in my head."