Unfortunately, there is no “good” place to put a first year official on a 5 man crew. Give them as much training and all of the support that you can. Help them understand that coaches and fans can be tough to deal with. And remember what some basketball coach said - “The best thing about freshmen is that they become sophomores.”
Having said that, we brought a 2nd year official onto our crew 2 years ago because we had to. I agree with Bama, but we also considered that the BJ is often the only official in position to make calls on deep passes and is always out there alone (maybe assisted by the LJ) on punts. We didn't like the idea of U for two reasons - the U controls the pace of the game as much as anyone and, more importantly, an inexperienced guy could get hurt in the middle if he doesn't know what he's doing. So that left the wings as options. Downside of HL is that he had to work the chains. Downside of LJ is that he's on the home team side with (usually) far more fans than the visitor side. After talking through all of that, we moved our experienced HL to BJ and put the new official at HL. Another plus for HL is that position is visible on almost every play on Hudl since film is taken from the press box, facing the HL. This allowed us to review and provide feedback after every game. It worked out well.