DrewPeterson7
Sage of the Order
This is all HUGELY subjective, of course.
That said... Start with the SM58, it's basically a 57 with a different grill and that's a pretty standard mic for guitar cabs. Generally, I've found an inch or closer with the SM57 is the way to go, and further back it gets very nasal and phasey as the room reflections play a bigger part. The 58's grill extends out in front a bit further, so you'll want to go even closer. Start maybe anywhere from touching the grill of the cabinet to maybe 3/4" off.
Straight on vs angled is also a matter of taste - generally, guys either go straight perpendiclular to the grill cloth, or angle it either about perpendicular to the angle of the speaker cone (say, 30 degrees) or about 45 degrees, same orientation. Again, try both, see what works for you.
Closer to the edge of the speaker will sound darker, while closer to the center of the cone gets quite a bit brighter. Again, there's no right or wrong as so much of this depends on the amp you're using and the sound you're after. I like a dark tone and play a Recto Roadster, so I'm usually within a band 1-2" from the edge of the cone, for rhythm guitar, but that's just me.
Basically, have fun, and see where you end up.
