There are aviation guarantees for Marine Option NROTC students that can be secured as soon as the second semester of your sophomore year.
Also, like gatordev stated, the purpose of NROTC is to graduate and commission officers. Obviously, if you don't graduate, you don't commission. So, classes that conflict with the ROTC drill period will take precendence most of the time. Generally, you won't be asked to volunteer for something or attend ROTC functions if it requires you to miss class. My unit even offers the chance for Midshipmen to be excused from morning PT a few times a semester if they have a test or a big paper due that day and they would benefit from the extra study time or sleep. Also, I know of many people in NROTC who have studied abroad for a semester. Bottom line is that it is in the interest of the ROTC unit to have Midshipmen go to class and make good grades. That said, you will be expected to sacrifice on occasion, and won't be excused from your 1400-1700 drill period because you want to take the 1400 Scuba Diving class instead of the 0800 class.
My opinion based on my ROTC experience compared to PLC:
If you are not on the 4-year Marine Option NROTC scholarship or do not pick it up after ~1 year of being a college programmer, PLC is a better choice.
I accepted the 4-year MO scholarship out of high school, so NROTC has been worth it for me. Because I have my tuition and books paid for, receive a monthly stipend ($250/month as a freshman, +$50 more every year afterwards) which helps but certainly does not cover my housing and living expenses, and have even received scholarships from my unit's alumni foundation totaling $3,000 during my time here, I can justify wearing the uniform to class once a week, getting up early a few times a week to PT, taking ROTC classes, and going to the 3 hour drill period every Thursday, along with the inevitable weekends spent fundraising, participating in drill competitions, or attending mando-fun events.
If I was not on scholarship, I would have a harder time justifying the work and time I put into ROTC when I could get the same commission through PLC.
I do believe the leadership development that occurs in NROTC is a significant benefit over PLC. The billets I have been assigned while in NROTC have given me an opportunity to develop basic skills like how to stand in front of a platoon and lead them in drill, or how to plan and organize events for 100+ people. Spending 2 summers in Quantico doesn't compare to the leadership and management skills you'll gain through 4 years of NROTC. Now, I'm not saying it's not something you can't get out of being in any other club on campus or quickly learn at TBS or soon thereafter, but NROTC certainly doesn't hurt your leadership skills.
And you only have to go to OCS for 6 weeks, no one wants to go back to that place a second time.
