So here is a follow up question to all of the answers that have been provided.......Have you tested any of these theories?
Have you tested a JHP vs an FMJ? Have you seen a difference?
I have. I have personally tested various loads and I can tell you this, for ME Personally, I cannot see a difference in accuracy for USPSA and steel challenge competitions. ( I don't shoot IDPA, but its basically the same thing target distance wise, so I will lump it in there with USPSA ). If you're talking about bullseye shooting, then maybe there might be a difference. But for USPSA, shoot what you got, or can get your hands on.
I shoot Montana Gold 124FMJ. I have thought about switching back to JHP for the closed base ( ie: no exposed lead ), but that is the only reason why. Not for accuracy reasons. It just never seems to be worth the extra money though.
Personally I think people shoot JHP's because they see others shoot them. Ironically enough, I think I see more people shoot lead RN than FMJ. I think these folks understand that there is no accuracy advantage with JHP's, and they feel the cost savings with lead far outweighs the perceived accuracy from JHP. If you're going to shoot 10,000 plus rounds a year, the cost savings will start adding up.
To the OP, go with what you like. You won't win or lose a match on FMJ vs JHP vs Lead. You will get more out of dry firing and practicing and having reliable equipment.
Right before I hit submit I had one more thought........
If you shoot Open...odds are you will want JHP. That is a whole other ballgame from what I understand. There is a lot of fouling in the comp that can happen with exposed base bullets or lead, so Open shooters I believe ( and I could be wrong ), prefer JHP for that reason.