i would go with airsoft, just because it can be more realistic to your firearms and equipment you use, can modify all the regular things you would on a regular firearm. just my opinion. With a paintball gun, you aim differently, and possibly limited to the types of courses available. With the airsoft you can practice many different simulation, your tactics, practice at home with paper targets, etc.
if you was interested in paintball, i have a spyder flash gun for sale. has everything but the mask.