You should attempt to go to STA-21 if you do not have a degree. It is by far a better deal (you get paid E5 salary to go to school+BAH with no other duties except participate in NROTC instead of going to school in your spare time around a time-intensive job) but it is also highly competitive.
Agreed that you need to have some good answers to your interview questions, as well as a stellar enlisted service record that includes volunteering for command-visible collateral duties (CFL, MWR President, EDTA, etc). This applies to both STA-21 and OCS.
I have not been enlisted, but I can tell you that the stress is "worth it." The thing that allowed me to wake up every morning at 0-dark-whatever and function in my job is every day was a chance to positively impact the sailors. As a divo, you won't be able to revolutionize their world, so don't expect that. But if you can figure out something to streamline their work and get them home a half out earlier every day, that's a victory for them. As you get more senior and display competence, you may earn your seat at the table at planning meetings (as opposed to ordered to show up and silently sit in the corner). That is where you can really have an impact on your division as you are the link between their day-to-day routine and the bigger events that the DH/XO/CO are thinking about, and that is where you have the most value to affect the lives of your men. The thing is, this will be transparent to your division.
The question that you need to answer is: do you want a seat at that table, or do you want to be the guy in Shaft Alley teaching your division how to fix an RO unit? If it's the latter, you want to be a Chief.
I can also tell you that there can be a LOT of politics in the Goat Locker. The Master Chiefs select their Chiefs, Senior Chiefs, and other Master Chiefs. In general, the Goat Locker tends to be tighter knit just because they collectively decided to stay in the Navy, and so they've all drank the kool aid and fully bought in to the culture, even the ones counting down the days to retirement. By contrast, a good portion of JOs in the wardroom will be counting down their days to get out and look at the submarine force as what the job they have to do to pay back their free college and thus think they are "too good" for the Navy. But that doesn't absolve either group from politics, at times pettiness, and their own version of a pecking order. Chiefs and Officers are human, too, and like any group of people who spend a lot of time together drama can occur. As for post-Navy retirement career opportunities, they are different. But you're getting ahead of yourself assuming that you will be able to make it 20 years. There are a lot of promotions between now and then that you have to earn, and a lot of sacrifices to be made on the home front.