What do you want it for, that should help narrow it down?
I prefer the Omni 4000 over the 5000 because it has a bigger cup and a lid for the cup to avoid spills.
The Badger 100 series is more of an illustration airbrush and can, in the right hands, spray even finer than the Omni's with the #1 tip and needle.
Mike
“Wisdom is the right use of knowledge. To know is not
to be wise. Many men know a great deal, and are all the greater fools
for it. There is no fool so great a fool as a knowing fool. But to know
how to use knowledge is to have wisdom. " Charles Spurgeon