Actually I use both. I started using an electric drill about 5 years ago and found that it is great for preparing teeth for crowns. It cuts faster, with less noise, more torque and less vibrations. My patients seem to prefer it to noisier air turbine drills and they say they fell less vibration. The vibration from an air turbine is produced by what dentist's refer to as "chatter". Most air turbines are floating inside a drill and actually move microscopically back and force while spinning. This translate to some vibration when these drill are cutting.
I believe the electric drill,due to their lack of chatter, cut not only faster but also more precisely than air turbine hand pieces. On the down side, they are heavier, and can be especially tiring for dentists used to the lighter air turbine hand pieces. Also they require patients to open their mouths slightly wider to accommodate the the larger head of the hand piece. This can sometimes be a problem when working on a back tooth.
I tend to use air turbines for work requiring a more delicate touch. I find that When using my air turbine, I can use my finger muscles to better guide the fine motions of this drill.
Consequently, I make use of both of these types of drills on a regular basis. Thier combined use tends to allow me maximaum flexibility and I think produces a better over all result.