"Smallest" needs to be defined. A 1 cu ft box for a 32" driver will still have larger dimensions than a 4 cu ft box for an 18" driver.
Same for "most powerful". One sub might take 10,000 W to get to full output, but another might match that volume with 100 W.
Same for "best". Lowest -3dB frequency? Lowest distortion under particular conditions? Flattest uncorrected anechoic response under particular conditions? Prettiest driver? Most output per $?
Sources/processing: stack of stuff that if it isn't vintage now, it will be soon!
Amps: stacks and stacks of old iron
Main speakers: big DIYSG
Surrounds: Bose graveyard
Subs: a bunch