I would say start with an electric. Typically it is easier to play than an acoustic because of lighter strings. Easier to bend and do hammer-ons / pull-offs if you want to play rock and/or blues. You can easily control the volume of the amp in case you don't wan't to disturb other people in your house. I know several people who started with acoustics and they end up sitting in the back of a closet.
Another thing to consider is the thickness of an acoustic compared to a nicely contoured body of a Strat, for example. The acoustic is not comfortable when sitting on the couch practicing and watching tv.

I have 7 electrics and 2 acoustics....guess which ones have dust on them....

just my 2 cents...