What is the difference between
9MM LUGER 147 GR Hollow Point/XTP
and
9MM LUGER 147 GR TAP - FPD
???
Also which one would make a better self-defense round?

i think either would work just fine.

here is what natchez has as a description for the xtp: Loaded with Hornady XTPª Bullets for deep, terminal penetration.Carefully selected high quality corrosion resistant brass cases for reliable feeding and to withstand maximum chamber pressures. Special selected high quality powders & primers for optimum performance.

and for the tap: Consistent pinpoint accuracy from bolt-action and semi-auto rifles. Reduced chance of collateral damage from over-penetration or ricochet. 100% Energy transfer to target, for instant terminal results and reduced need for repeat shots. No tip deformation caused by administrative loading & unloading of the weapon or impacting of the tip in semi-auto magazines under recoil.

So it is basically the same thing from what it sounds, besides from the coating on the brass. Is it really a gimmic to make a few dollars more on the TAP?

one might have a deeper or wider hollow.  one might have a bonded bullet.  i am really not sure but if it were me i would buy the cheaper and if it fed through my pistols then i would leave the expanding part up to the round and i figure hornady would do that right.  

As noted in the TACKED topic atop the AR15 Ammunition forum, here are top performers for 9mm:

9mm
-Winchester Ranger 127 gr +P+ JHP
-Winchester Ranger 147 gr JHP
-Speer Gold Dot 124 gr +P JHP
-Remington Golden Saber 147 gr JHP
-Federal Tactical 124 gr JHP
-Federal Tactical 135 gr +P JHP


Realize your asking about the Hornady XTPs, but thought this might be of interest to your "best self defense round" issues, as the Rangers are pretty popular............

Mike