Well, the type of air compressor you buy all depends on the use you have in mind. For smaller jobs, an electric, either battery or main operated unit should do the job. For larger jobs a two stage gas compressor is probably your best choice. As for horsepower, most companies make compressors of about 2 to 30 horsepower, once again the power you choose should be relative to the task in hand.
Personally I would recommend the company "Ingersoll Rand". They offer high quality units at competitive prices. Also they have a large range, sure to cater to your particular task.