For FOH, I rarely, if ever, use compression for acoustic guitars. Piezo pick-ups already compress the dynamic range of an acoustic guitar to an unnatural degree. If the player is using a magnetic pick-up then perhaps I'll use a small amount of compression between 1:2 and 1:4. I've found that most of the performers using magnetic pick-ups that I mix for are fingerpickers and really don't like having compression unless it's very light.
I use the TC Electronics M-One's M-One Magic (I think that's what it is) preset for acoustic guitar. The delay tapped to the tempo of the player is simply excellent and the voicing of the reverb is perfect.
From a player's perspective I am very much a purist. I know what sounds I want from my acoustic and I coax them out of it without the use of any special effects. I will use the occasional modulation and delay if the song calls for it but that's about it. Of course, a trusty TC reverb is always on for my guitar.