There are different critics for choosing the paints, here you have some of them:
Inside or outside?
Quickly or slowly?
Which effects/Stye are you going to use? (Some prefer drippy paints,oldskool or newskool outlines...)
Color choice?
Can control?
Amount of surface to fill-in?
Commissioned work or not?
Type of surface?
Temporarily painting or long-lasting painting?
Weather/exposure conditions?
Addiction to a spraycan brand?
Collector item or not? Some also collect different spraycans...