I use a small diaphragm condenser like a Shure SM81 or an AT-4041 aimed at the treble screen for my '30s Regal, which has a fairly mellow sound. If I want to minimize the treble, as when recording my clangy '84 Dobro, I might use a dynamic.
It depends on how big the room is, too (among other things). I have sat with my reso and gone through my arsenal of mics a couple of times, doing A/B (and C/D/E!) recordings to figure out what sounded best.
If you don't need to close mic, a large diaphragm condenser's fine, too, but again it depends on the room. I'm an old electric player, and I don't like a lot of air around the guitar, so it sounds dryer, and I often play ensemble, so I use a closer rather than farther mic placement.
i havent tried sm57's yet, I have been using MXL 990. the room is a bit larger, with low ceilings. There is a small section of the room that is under a staircase that I have turned ito somewhat of a vocal booth, would that be better?