Zoom 505
I have a Zoom 505 and never use it on my acoustic. I very seldom use it for my electric. They are ok to play with and maybe useful in a live situation. However, for recording purposes, they are far to noisy. I get a lot of hiss from it, making it pretty much useless.
When playing live, using an acoustic or keyboard amp is great. However when recording I usually go direct in conjunction with micing the guitar.