When choosing a garbage disposal, you need to consider cost, warranty, and the food types you will normally grind with the disposal. If you often grind bones then consider a more powerful motor such as a 3/4 hp or 1 hp model. Otherwise you should be fine with the standard and less expensive 1/2 hp motor.
Other considerations to look at for new installations are the electrical connection, location of the on/off switch, and piping. For best results, call a professional to install your garbage disposal.