I can only talk in general terms, because every situation is different. I've had my best luck with steel string acoustic using one large diaphragm mic somewhere near the 12th fret, maybe 8" out. I've had my best luck on nylon strings with a small diaphragm pair X-Y, backed off 4 feet or so. I really don't know what it is sonically that makes those setups so different, but the setup for nylon just isn't the same as the one for steel, for me. The general rules are: 1. Almost any combination of 2 mics can work. 2 SD, 2 LD, one of each, or even a dynamic and a condenser. Ribbons can be very good, but....
My guess is that a man with one SM57 probably isn't planning on spending $2000 or so on a mic at the current time. The guys have mentioned a few cheap standards that work. MXL603, MXLV67 (yes, on acoustic), Studio Projects B-1, CAD M179 all come to mind.
But this brings you to rule #2- All other things being equal, the more you spend on mics and preamps, the better it will sound, and as the price goes up, you will get less and less improvement per dollar. Diminishing returns, so 65% of the money is spent on the last 10% of performance. You have to decide what you're willing and able to spend on sound, and then live with it.
I think it's interesting that some folks like the Dragonfly on acoustic. I wish I owned one, but I'm not very fond of the Kiwi, which I do own, on acoustic (it's a pretty good vocal mic for the right voice). I've gotten more usable acoustic tracks with a C414. But here we're talking $600-$800 mics. In the budget world, here's my rule #3- Use small diaphragm mics on good guitars and large diaphragm or colored mics on cheap guitars. If you have a nice guitar, MXL603 is a good choice. If you play a beater, try AKG C2000B. Under $200 with the shock mount, it's a versatile little bugger. It's a side addressed small diaphragm mic in a larger housing than a pencil mic, which makes it a pretty useful vocal mic, as well as being good on guitars, especially cheap ones. It actually makes an Ovation sound pretty good, which means, to me, that it's not that accurate. That's why I like it. It's like makeup. Sometimes you'd rather hear a pleasing illusion.
Finally, you are stuck with rule #4- If the guitar and the song and the room and the player do not suck, your recording probably won't suck. The room is huge on effect. I don't like acoustic in dead rooms, and I don't own the high end FX boxes it would take to recreate a good sounding room. I also lack the expertise. I am lucky to have a pretty good live room, requiring minimal treatment to get good sound. The sound of the room is a key. Best of luck-Richie
