On a more serious answer....
First: I'd buy used if you can. More bang for the buck. Or, if buying new, from now until Jan is the best time, as dealers blow out last year's stock to make room to order new models at NAMM show in Jan.
Second: Figure out which speaker type/size/configuration you get the sound you like best from. Go to a music store and try out 1x15, 2x10, 4x10, etc. Aso be aware if they have a horn/tweeter/attenuator control on the back.
Third: Once you figure out the configuration you like best, make sure it fits in your car along with the other gear you use and might have to transport to gigs or rehearsal. If it doesn't fit, you might want to reconsider something that does fit.
Fourth: Make sure you try our cabs WITH THE SAME MODEL HEAD and the bass you use. Not all cabs sound right with certain heads. Best to use your own bass too.
Fifth: More expensive does NOT mean "better." If you like a certain speaker cab, ask on forums if there is a similar less expensive equivalent.
Sixth: (Gonna get flamed here...) No matter how much you try to perfect "your sound".....once the rest of the band starts playing at a gig, ten feet past the stage no one will be able to tell the difference. And past the ten feet, it will depend on what the soundman does to your bass signal. It's mostly all a big evil marketing scam to sell gear