I know the 57 and Beta 57 are the "standard" for guitar cabs for many years. However, I have to be the only idiot in all of “guitardom”who never liked the sound of a 57 on a cab. For my taste, the highs always ripped my face off, or if not too bright, it would be too muddy and not tight and defined. I know a good deal about mic placement from our studio, so I've tried many things... but still was never happy. I used to use a combination of a 421/57, 414/421 and I had to fight to get what I wanted. Then there were the phasing issues if they were too far apart. I also did not want to have to do a ton of salvage EQ on the native sound, I wanted to get my sound down and then use the EQ to enhance and sculpt, not correct mistakes made by incorrect mic choice and/or placement.
A few years ago I got a matched pair of Royer 121 Ribbon mics. The Royer 121 was a game changer for me. The ribbon sound is warm, organic, and still BRUTAL if you want it to be. It also sounds like your cab, not too colored. For crunch guitars it totally kills! We use them in the studio and we use them live too. I get an amazing sound with minimal passes at mic placement...in 10 mins I have my sound every time After I got them, I never looked back...not interested in anything else..
Mic Placement - whatever mic you use, and assuming you are after a fat crunch sound that will not rip your face off with the highs or presence try the following...close mic at about 2-3 inches away from the grill cloth. Do not point the mic directly at the cone go for the edge of the speaker, unless you want it brighter. Also, angle the front of the mic a couple of inches off to the side of the grill, not directly into it---off-axis. Do this to taste.