On the opposite end of the mic spectrum, I've dealt with two UST's, Fishman Acoustic Matrix and L.R. Baggs Element, both active pickups. I like both, but they are decidedly different, both in sound, and technology.
Fishman is pretty standard for a number of builders, and a lot of artists are accustomed to the sound of a Fishman. After hearing the L.R. Baggs, the Fishman sounds quacky (but, that could be part of the technology and the active pre-amp). However, common comments from artists that move from Fishman to Baggs is the Baggs is not "there". Fishman seem to be more sensitive, and installing them requires less critical setup than the Baggs. The old Matrix needed to be soldered - the new ones are plug and play, with a soundhole volume control (old ones were an addition).
That being said, I've switched to L.R. Baggs. Its supposed to be "plug and play", but I custom order the pickups with nothing attached (so, like the old Fishman, it all has to be soldered). This is fine by me because I order the actual UST wire shortened for the `ukulele, as well as the battery and volume control (I just shorten those myself, but they come in unattached). Like Fishman, Baggs has two types of preamps available. Whereas Fishman gears theirs towards body size, Baggs designs for string type (nylon or steel). Obviously, the Nylon is a no brainer. In addition to all the soldering (which is not necessary if you just order it stock), I feel the design of the UST itself is more finicky to installation than the Fishman; meaning, every little thing can affect operation, such as, saddle fit, flatness (bottom), saddle slot flatness, proper tying off of the element, etc. The one panacea I've found is something that Rick Turner came up with, and that is back angling the saddle for proper compression of the UST once its strung up. The best way I can describe what this does is with a comment from Paul Okami - he stated that the pickup was installed "without incident."
So why switch even though (for me) it requires more effort? Sound. Personally (and my friends say the same), the Baggs sounds the most natural, really. And, its worth the effort. I'm not the only one that feels this way. Lots of builders here are installing Baggs (instead of Fishman - of course, now Fishman has the new Matrix Infinity so that may change again).
L.R. Baggs must be doing something right - they supply the actual UST for other companies, like D-TAR and MiSi. I've heard the MiSi and the D-Tar. Not sure I buy the technology of the MiSi, yet (but that can change), but Rick Turner demoed a Compass Rose installed D-TAR and banged (and I mean BANGED) away with no distortion whatsoever - just clean, natural, and loud (because the amp was cranked). I guess the 18v system with outboard batteries and the stereo cable connection (among other things) is the trick. I've seen it, played it, heard it, it works great.
Of course, there is one that that will not change - if you have a crap sounding instrument to begin with, a quality UST will not make it sound "electric", it will make it sound crappy, really loud.
Guess that was more than $.02, huh? -Aaron