Well, I have all 3 drivers here... and in the following enclosures:
FE126E - Ed's Hornshoppe horns
FX120/F120A - 10-liter ported enclosure on stands.
First, the FE126E is a different animal from the other two... higher sensitivity by a good margin but much less expensive with a stamped frame and ceramic magnet.
The FX120 and F120A shared some common components: die-cast frame, cone and alloy dustcover (different color on front, rear is the same). The main difference is the magnet assembly, the F120A being alnico and over twice the price of the FX120.
So, how do they sound (in my view)?
FE126E - well-known (all around) performer, very good bang for the buck and is flexible in varied designs. It's get loud with little input.... but I don't like the fact that it develops what I call "upper midrange shout" if driven too loud (starts shouting at 1-watt).
FX120 - an expensive driver (~$106) with a nicely done die-cast frame, cone assembly, etc. with a large ceramic magnet. Less sensitivity (so more power required for similar levels) but a much flatter response. Also note different enclosure... not recommended for a rear-loaded horn. In short, a more refined sound IMHO. Less fatiguing for long listening periods and better resolution.
F120A - a very expensive driver at ~$227 each. Main difference from above is the alnico magnet assembly, but the surround is also slightly different. Overall freq response similar but a bit flatter and rolls off a bit earlier on top. Sonically, this is significantly better! Alnico retrieves the low-level detail much better. You just need more power with these, 8+ watts but SET preferred. These are my first choice (small) Fostex drivers, but alas only 89dB.
Regards, KM