Mustangs, which was worse, Boot Camp or OCS?

Congratulations to you, Captain, for enduring both boot camp and OCS/TBS to get what you wanted. The best officers I served under were mustangs - they did not forget where they had come from. I did not travel that path, remaining enlisted, but I had some peripheral experience with officers going through The Basic School. When I returned from Vietnam (Mar 69), I was PCS'd to TBS, where I was an enlisted instructor on general weapons. That meant after the primary officer instructor finished his class and the 2d Lts got on the weapons, we supervised them and further instructed them in the weapon's operation. Being salty Vietnam vets (and most combat vets as well), we had a good time messing with the new lieutenants, since they were pretty naïve about the Corps at that point. The only ones we didn't mess with were the WO classes (former enlisted SNCOs who'd kick the crap out of anybody messing with them) and mustang officers (for pretty much the same reasons). I don't think officers who were appointed through the LDO programs had to go to OCS. I once knew a Gunny who accepted an LDO-2 commission as a 2d Lt (with a terminal rank of Captain) simply because all he ever wanted to be was a Captain of Marines. As to your DIs going hard on you because you chose the mustang path, I recall that as a DI at San Diego, we used to go harder on recruits with prior enlisted experience in the other services - and some of them were real pieces of work!

PI was a blast, WOBC a requirement, but I did go through NCO Course at OCS Quantico. My guess would be OCS is harder. Especially when Col. Fox was CO. We ran all the same trails and courses as the candidates. The creek was near frozen for Quigley. Royal Marine Colour Sergeant PT instructor. PI was a mind game with a solid harassment package. Especially 3rd BN.

I would say OCS was more physically demanding while PI was more of a challenge mentally. The "shock" level was less at OCS, perhaps because I'd learned to put it in perspective at boot camp. I do remember telling my rack mate at OCS to relax; although they seemed to want to kill you, they wouldn't because of the paperwork. He credited that comment with calming him to the point he made 50 years later at our reunion.