When you were a GySgt facing promotion, were you able to choose between MSgt and 1stSgt? If so, what influenced your decision?

There is (or was) a box to check on any GySgt fitness report (FITREP) for consideration for promotion to 1stSgt. Putting in for consideration does not necessarily mean the individual would be selected, but that is where you made the desire known.

For me, I did not check the box. I was in a technical MOS and, by virtue of my career path, had been exposed and maintained far more detailed technical knowledge than pretty much any of my peers. To go the 1stSgt route would not have made sense for me or benefitted the Corps as a whole. That said, I worked at one point with a stellar Marine GySgt who maintained adequate technical knowledge, but he bled scarlet and gold. He would have made an outstanding 1stSgt... but still, he was not selected. The process is not always perfect.

Generally speaking, those that go the 1stSgt route have done time on the drill field and consider themselves (and considered by others) the keepers of the institutional culture of the Marine Corps. They aren't just berating you for minor uniform infractions because they enjoy it... that is the burden they must carry by virtue of their career path (and because they enjoy it).

Those that go the MSgt, MGySgt route, on the other hand, are the technical professionals of their field. They will often refer to the 1stSgt, jokingly, as "unskilled labor", and enjoy reminding the 1stSgt that they can do the 1stSgt's job (MSgts will sometimes fill the 1stSgt billet should it be gapped), but the 1stSgt can't do their job.

In reality though, a good 1stSgt is worth more than their weight in gold. They can make or break a unit. A unit with a solid functioning 1stSgt can run smoothly with good morale, even with a poor commander (usually). A bad 1stSgt, on the other hand, can grind a functioning unit to a halt, crush morale, and generally make every day a burdensome existence. One can not overstate the importance of the 1stSgt position. Only the best need apply.

I had the opportunity to fill in as a 1stSgt on two occasions, and was recommended by two SgtMaj's that I should go the 1stSgt route. Ultimately, I didn't like the job and elected to be a MSgt. And, yes, I don't regret it for a second.

This is a great question for 1stSgt (Join to see).
My understanding of the process is that they select on the their FitRep where they want to go the Leadership (First Sergeant to Sergeant Major) or Technical (Master Sergeant to Master Gunnery Sergeant) route, however the "needs of the Corps" are a/the determining factor in actual selection.