The Harmony Soundhole pickups have come a long way and many of them do now make a good imitation of an acoustic guitar sound. I suspect they use different magnets and windings to those on an electric pickup (or maybe I just believe the marketing!). Some of the now-standard undersaddle pickups sound a bit tinny or quacky

Some soundhole pickups like the Sunrise (used by Emmylou Harris, Richard Thompson and others) and the Baggs M1 Active also pick up soundboard vibrations rather than just the strings. John Prine uses a Dean Markeley which I think is a purely magnetic one. Seems to use this on one guitar for fingerpicking and it sounded good when I saw him live. I have an Artec MSP50 which is very similar in construction to the single-coil Fishman Neo-D, but a fraction of the price. It sounds not at all bad when picking arpeggios, less so for strumming.

Preamps can increase volume but also match the impedance of pickup to that of the amp. I only vaguely understand what that means except that some pickups won't work so will with some amps withbut a preamp.
User reviews of all pickp types can be found here http://www.harmonycentral.com/user-reviews/