2-way speaker with best bass

Talon Raven-C

Aspara Acoustics HL1 have lovely bass.

Usher BE-718 tiny dancer. Excellent bass qualities on this speaker. Check reviews for more details.

The original Large Advent has bass appeal I've never heard bettered. If units sold is a valid measure of most successful, these are da bomb.

The problem of bass is that it requires a large driver and a large box. The
problem with midrange is that you need a small driver to produce this
properly - that is without "beaming". You can get prodigious bass
by adding ports to a small woofer but it won't be musical - mostly one note
bass. To get decent bass you need critical damping. To get decent mids you
need proper dispersion (not beaming) and a dome tweeter would be good for
dispersion but it can't handle the excursion necessary to crossover low
enough to a big woofer.

This is all physics.

Given the constraints - there are several ways to go about it.

1) A large driver with a whizzer cone - the draw back is distortion and a
bumpy frequency response in the mids.
2) A small but very powerful woofer (6 inch) in a sealed box with a large
phase plug or dome to control dispersion better in the mids. (You still won't
get much bass but mids will be better and what bass you get will at least be
accurate)
3) A large driver for bass and with a single horn for mid and tweeter. This
allows you to
crossover low down so you can avoid beaming from a big woofer. You get
good bass and great mids with a gentle roll off in the highs. All round pretty
good except you now have your crossover in a rather critical range (700 to
900 Hz)

Thats pretty much all folks - only so many ways to skin a cat. You can play
with TL and bass extended ported designs until the cows come home but
IMHO you will never get the "best" bass response that way.
Although to many people "best" may simply mean "prodigious" - in which
case anything is possible.