Boy, you sure picked a ripe subject here, West!
Everyone weighs in differently on this one. It may have to do with the sound they want, or just convenience factors. I struggled with this for a couple of years now. I sampled Fender Acoustisonics, Strawberry Blondes, Marshall's A100, Carvin's counterpart to Fender's, and a few others. I was looking for something I could use at a solo gig with an axe and a mic; easy to transport. I really couldn't notice much of a difference between any of them. This is most likley because I don't play well enough to make a differfence. A couple months ago I settled on a small mixer by Yamaha, the MG8 with digital effects, and I push it with my old Crown amplifier through home-built 12" speakers. Nothing convenient about it -the mixer weighs 4 pounds and the amp weighs 28. But I do like the sound and I have a lot more features and flexibility if someone comes by to sit in, which does happen from time-to-time. I've heard good things about the Genz-Benz, too, but I haven't met anyone who owns one. Pricey. Then again, I've also read a review or two about Behringer's acoustic amp which seems to have every feature in the world for about $99USD.
I think all you can do is try a bunch of 'em in circumstances close to what you'll be playing in, and trust your own judgment.
I'd also highly recommend reading Dan Crary's "rant" about amplifying acoustic guitars on his website:
http://www.dancrary.com/danrant/danrant_2001_10.html
BTW: How'd I leave him off my list? The first Taylor signature model was made for him. He has a grammy-winning album. And he was a thorough gentleman when I was able to book him for a little bluegrass/gospel festival I put on several years ago. If only he played Guild!
Guildmark
PS - If you're looking at the Genz-Benz, 'cause maybe price is no object, check out the Bose tubular job. Very interesting!