Kind of depends on what your interests are. IMO VTR is more focused on all aspects of Triumph ownership, including modified cars, all models and camaraderie; while TRA focuses more on strict originality, including concours-type shows, and only for the TR2-4A range of cars.
While I do try to keep my car somewhat close to original in appearance; I do like making small modifications to make it more practical to drive on an every-day basis. (Before I retired, I drove it to work every day unless it was raining or the car was broken.) I'll get flamed for this, no doubt, but I also dislike the snobbery of suggesting that a TR5 (for example), is somehow lesser because it doesn't use the old 4 pot "tractor" motor.
Strictly IMO, YMMV, etc. Hopefully there is room for all in the hobby, those are just my preferences.
PS, I believe the current TRA judging guidelines are no longer "free" to non-members.
PPS, you might want to look into a local club instead of national, like
https://www.cptc.org/