What situations are you playing in? Solo? Band? Large or small venues? What kind of music? Folk? Rock? Country?

If you're not playing in a band, the K&K Pure is pretty much the most natural 'acoustic' pickup around, nothing under your saddle to bollocks up your 'unplugged' tone, it's passive so no heavy battery in the guitar that could leak or will need farting around replacing from time to time. It's a pretty 'hot' signal for a passive PU and it's quite possible to do without a pre-amp, but its output impedance is 1 megohm, compared with the UST's usual 10 megohm, so a suitable outboard DI/pre-amp like the Orchid Muting DI, or the Orchid Acoustic Pre-amp is desirable for the purpose of matching the PU output impedance with the input of a PA.

I have K&Ks in my Martins (HD-28V and OM-28 Marquis) and in my Lowden, which I put through either my Orchid Muting DI or Orchid Acoustic Guitar Pre-amp, and I get a lot of comments about how great all three sound. I'm doing solo folky-type stuff.

Orchid Electronics

K&K Pickups

If you're playing in a band and working at high volumes, a UST such as a Fishman or, if you want to go up-market, a Headway or Highlander, would be a better bet from the feedback viewpoint. As I haven't used USTs for a few years I can't really comment any further about them (other than to say I don't like them much!).