Airbrush bottles comes in glass or plastic. The advantage to glass is that it is easy to clean and resistant to solvents. Plastic bottles don’t hold up very well with solvents unless they are made from solvent-proof plastics, in which they are not clear so you cannot see the exact color in the bottle. On the other hand plastic bottles are lighter and wont break if you drop them.
The metal adapter caps are popular but keep in mind that they will eventually where out the siphon area of you airbrush if used regularly. Plastic caps will have less wear and tear on the airbrush and if you get the Fast Cap version there will be less clogging.
For added security Paasche makes screw on bottles that bolt directly onto their VLS and HS models. These are good for muralists and decorators who are working on ladders and such.