Bob prefers a Shure SM57 pointed off-axis from the speaker cone and almost touching the grill of the cabinet, but not quite touching as you may get a buzz in the recording.
Single Mic Setup
Two Mic Setup
Coupled with his off-axis Shure SM57 on one cone, Bob uses a Royer 121 or another ribbon mic close to the other cone. The closer to the ribbon mic is to the cone the more 'warmth' you'll get in the recording.
Electric Guitar Tracking Trick
This is a cool trick where you use two mics pointing in opposite directions and a hard surface to get a larger guitar tone. Watch Bob talk about it below.