What's the best bass speaker

What's the best bass speaker an 18' or 21'! A for the 18' what is the best bass bin scoop and for 21' what is the best 21' bass scoop. What of the two sounds best

There's no best 18" driver for 18 inch scoops, it depends on the design really and the different person/s tastes.

I don't have any experience with 21" drivers or above in scoops.

But for 18" drivers in scoops, the most known contenders are:

Fane 18XB, PD1850, Void V-1800, Turbomax 1500i.