There are some great pickups on the market these days. I would avoid the mics because they can be difficult to manage.

They each have their advantages - the under saddles can be best compromise; good sound (if somewhat "quacky" as reported above) the I-Beam can beautiful, especially if blended with an under-saddle (LR Baggs makes a beauty like this) and I love the sound of the sound-hole magnetic pickups - but they DO sound electric (no surprise). A lot of fine finger style guitarists blend the magnetic pick-up with a floor mounted mic (for the highs) and this can produce a lovely sound.

BUT - having said that, the best modest price solution that works well on most guitars and is a pretty mature (well developed) product would the under saddle types from; PickUpTheWorld, Fishman or from LR Baggs. I've used all three of these and all three of these companies have a variety of excellent products.

I am especially fond of the LR Baggs i Beam and under-saddle blend. It's cheap, versatile, easy to use and has a truly remarkable sound.