I prefer to plug directly into the PA, via a Baggs PADI, and hear myself through the monitors.
But, if that's not an option (having to use a less qualified drummer, who doesn't understand dynamics, for instance), then I like the Crate 60 or 125 watt acoustic amps, and run them into the PA, so that the amp essentially becomes my "guitar monitor".
From my soundman perspective, or when I'm playing with pro sound provided, I'm a firm believer in just go DI.
I'm asking, though, for my musical partner Julie. We often play shows where there's no PA provided (she then uses her EONs on a stick for vocals only), or there's a PA but no soundman, or no monitors, all the usual problems you expect at small places.
So it's good for all of us in those situations to have our own small amp to hear ourselves, especially her as she likes an inordinate amount of herself in any monitor provided. Having her acoustic through the monitor also will cause our backup singers to stop singing or possibly vacate the venue. Having her acoustic through a little amp behind her and not facing the rest of us works well for us, usually.
So we're looking for a solution that fits those varied parameters, which may include buying a little acoustic guitar amp, maybe a pedal of some sort to get the best tone, and definitely a better guitar for her as she currently plays with an inexpensive Fender acoustic that we had to glue the headstock back on recently.
Terry D.