AJROTC is usually a class. Usually the only homework you have for that is clubs (drill team, color guard, rifle team, rappel master, scuba, summer camp training, raiders, etc. etc.) and getting your uniform ready. You still have to study for in class tests and such, but you usually don't have any realy homework.
Sea Cadets is something that can be a little more time consuming, going on my knowledge with Civil Air Patrol. As you progress in grade/rank and get higher in the chain of command, and more responsibilities, it will require more time.
I keep up 3 honors classes - Hon English II - I am currently researching a debate, studying 90 words for a vocab test, reading a book - answering questions and lookin up the 15% of all the text words that I don't know. Hon Alg II - homework every night. Honors Chem - lets put it this way, this class is hard. I was active in the Marching Band, and SADD, Octogon Club, and Astronomy Club (hey, we get to have star parties [insert dancy smiley here]). I still managed to keep up my Cadet Commander position at my squadron. It takes some give and take (doing homework in spare time at meetings (after tests, other rare occasions), homework in the van for missions or training, homework when I wasn't teaching at Basic Cadet School, etc. etc.) and taking 7 tests in one day can be painful when it comes to the last two being at CAP (I failed my first leadership test that way), but I manage to do it.
It is really up to you, and how you manage your time. If you don't have time consuming classes, aren't addicted to the internet, and are good at managing your time, you will more than likely do very well in both. Just don't let your grades slide, because if its anything like CAP - you must maintain a C average, but I don't reccommend it, and no one likes it.
Good Luck and I hope your decision works out for you!