Acoustic-electric guitars

I am considering buying an acoustic-electric guitar. But I wonder, since there is a number of pick-up elements (single-coil, piezo, Baggs), will it make more sense getting an acoustic guitar and then installing a pick-up on it? Anybody has experience upgrading your acoustic to acoustic-electric? Also, what's the difference IN THE SOUND of various systems of pick-ups for acoustics?

Get the electric-acustic one, I have an acustic and I'm thikng of installing a pickup on it but thats cos i already have the acustic, if didnt have anyone i would go for the electric acustic, because the work is done already.