I have RCBS carbide dies, and the seater/ taper crimp comes with a seat for ball and flat tipped rounds.

I tried using the flat tipped one to seat my Horniday JHP's and a few were flattened out even more and had a slight seperation of lead/ jacket. I have since tried the ball seat and have noticed a vast improvment but still a few, though hardly noticable, deformed. Should I just choose the lesser of 2 evils and keep on with the ball seat?

Are you talking pistol or rifle?  Need more info please.

And pics would also help.

There should be no distorting when seating JHP no mater the seater plug.  If you are getting deformed and distorted Jacketed bullets then you have a problem with the die itself and the way it was set up.  My guess would be that your have the die set wrong and are over crimping while seating the bullet.

 How did you set up your seating die, in detail please.

Read the instructions included with your die set and you'll find something to the effect of "RCBS knows that the included seater plugs probably won't fit any bullet known to man, but we will custom make one for $16.95 + $4.50 s/h". RCBS does have some standard order plugs for specific bullets(gold dots and a couple others).
I just got in two custom plugs for some of my cast bullets. What bullet are you trying to use? Use the flat(semiwadcutter) plug for the hornady's unless you get a custom plug made. Alternatively, buy a hornady seater die.





ETA: the reason I suggest the flat plug is that bullets should seat straighter with it than the round nose plug. What cartridge are you loading? I can't remember any XTP I've ever used requiring enough force to deform the bullet. Are you using the expander die and belling the case?




 

I can't imagine having to exert enough force on the bullet to have it expand during seating.

They'll also seat to pretty much the same depth. The RN seater will vary the OAL of the cartridge because of the differences in the mouth of the bullet. I'm currently running into this very issue with RCBS's dies and Berry's 124gr HP 9mm. My COAL's are varying by .015".

And once again AeroE nails it. Many HP designs can be seated and crimped in one step, but many are soft enough that you want to do it in two steps.