I use a Neumann KM184 mostly on my Ramirez 4E. On it's own it's a great mic (and pretty much industry standard for recording acoustic guitars). I'll tend to aim it at the 12th fret, about 6-8 inches away. Usually I'll pair it with a Rode NT1 pointed back at the bridge area, but if I had to use only one it would definitely be the KM184.
For fun? Doesn't matter that much. Any decent one is fine. Be prepared for a sharp learning curve on distance, directional placement, selecting a room, etc. no matter what you get. It's an art to pull it all together.
Well my budget isn't able to handle a Neumann, so I once did a Christmas CD for family members on a good ole' Shure SM57 into a digital recorder. I played both nylon string and steel string pieces. I recall adding a vocal mic to reinforce the sound and that worked well on a few pieces. I used a Sennheiser e935 at a slightly lower volume and it widened the sound a bit.
I've been using a Rode NT3 for a few years. It's a very good mic for acoustics. The only knock is that it doesn't have a bass cutoff switch, which is why it's less expensive than other models of theirs. But I'm always fiddling with bass level on the software EQ, anyway (especially for nylon strings), regardless of the mic. And it's small enough to use for gigs, too, which is a nice perc. So the bass cutoff is a non-issue for me.
Here's a recording I made on my nylon string through the NT3. The mic was tilted very slightly up, pointing at the soundhole from about 8 inches away. I've found that this is a good alternative to the standard 2 mic setup: