I was just wondering, the sm57 seams to be the mic that most artists use for their Guitar Cabinet, but is it really the best mic for that or is it just that it's been such a classical model so long that they just presume that its the best and therefor use it?
There is never a "best" microphone. Is there a "best guitar amp"? Is there a "best guitar"? The selection of a mic, guitar amp, or guitar is subjective. It is what appeals to your ear that is important. Many artists prefer the sound of the SM57 for miking a guitar amp, thus its popularity.
The SM57 has been internally improved in many ways over the years, but the styling has stayed the same because customers like it. Some styles are classics: Marshall amps, Fender Telecaster, Gibson Les Paul, Shure SM57 and SM58.
Try the Beta 56 or Beta 57 as a "step-up" from the SM57.