I know many people are very happy with the results they get from some very good electric guitar amplifiers, but I'm 100% with Pippin on this. A decent acoustic amplifier makes a world of difference.
An acoustic guitar amplifier would be my weapon of choice every time.
Marshall acoustic amps are great. I use a 50w Marshall as my working amp, and I'm extremely satisfied with it. I'd say the Marshalls offer a nearly unbeatable combination of sound, quality, features and affordability. With the help of a small mixer I sometimes use mine as a mini-PA for 4 or more people at very small gigs!
There are better amps out there, but most of them cost several arms and several legs.
A mate of mine has a lovely
Carvin acoustic amp, and another has an
AER acoustic amp.