Wow! this is a tough question, seriously! On one hand, the beginner wants to see at least a few early results, especially when they love rock and roll, and not folk music. But on the other hand, an acoustic does build the chord progression/rhythm skills greatly. I wish I had spent more time on the acoustic, as there are so many great songs for the acoustic that dont sound right electric, such as side B of GnR's Lies album (man I am showing my age!), as well as Godsmack unplugged... I have used both, and I practice in proportion to the amount of acoustic songs found on a typical rock album, usually one per 8 or nine songs, regarding between switching between electrics and acoustics, as far as time goes. Remember, it's music- it's what you feel like playing, though, and some days you just don't want to play heavy. I have to admit, there is nothing like learning how to play one of your favorite sabbath or some 70's aerosmith electric solos... it feels more satisfying to learn that than 'american pie.' Good luck!