Minefield!
Pretty much the industry standard is the
3M "fly mask" 6941 , found in bodyshops everywhere. It offers a good level of protection and has tons of adjustment for a good fit on most faces. It's recently been upgraded to the 6941
+ which has a better exhalation valve, but I've hardly noticed the difference myself so don't worry if you can only find the previous version.
If you want to go for the replaceable cartridge type, then the
3M 06782 is a decent choice. It has separate filters for vapours and particulates, and comes with 2 sets in the box.
My personal favourite would be the
Moldex 7000 . I have the previous 6000 series and find it a bit lighter and more comfortable than the similar 3M. It also has an easy quick change system for the filters so you can remove the vapour filters and just use the particulate ones if you are sanding for instance.
You can also get full face versions, like the
3M 6000 or
Moldex 9000 series that protect your eyes from the irritation that can be caused by organic solvents, but for airbrushing I think they are OTT unless you are particularly sensitive.
Always keep any mask (or the filters) in a sealed bag or container (like a tupperware box) when not in use to prolong the life of the filters, and bear in mind that these masks are only rated for clean shaven folks, as beards can interfere with the face seal. At the concentrations we work at I doubt it will be a problem, but thought I'd mention it.