I started a thread on this topic in the amps section - it's a good thing to discuss!
Being in the ad music business for a long time, and doing lots of guitar sessions, I'm using a lot of Royer R-121, SM-57, and even Audix i5. For clean amps, the Blue Dragonfly is a very good mic, it's like having the amp in the control room.
The Royer's very fast transient response gives the mic a very three-dimensional quality, and the inherent darkness of a ribbon tends to offset fizz and somewhat spiky speakers (looking at you, Celestion V-30s!). It also takes EQ very, very well, because there is very little distortion in the signal of a good ribbon. The Royer also has a ton of low-end proximity effect, that can be manipulated if one desires a "big" sound. Very good for high gain work. The mic can also be flipped backwards for more brightness. The bidirectional polar pattern picks up room sound, so people tend to think it sounds like the amp in the room, and there is a little of that, though it's not the main reason I like to use them.
The 57 is the classic mic for a reason. It sits in a mix very well. I like the i5 for similar reasons, and it has a little more accurate bottom end.