Seven reasons you don't want to march with a baritone sax:
1. It's really heavy and marching with it (especially any modern low-A horn) is rough on your back unless you're built like a football linebacker.
2. Marching bands usually like sax players to have their horns in front of them. If you're playing a bari, the body mechanics involved in doing that are awful, and you're just begging for hand and wrist problems if you do a lot of it.
3. Baris don't like being knocked around, which comes with the territory in a marching band. And believe me, there's nothing more exasperating than discovering that some idiot banged your horn and rendered it unplayable when you're on your way to an event.
4. Most school-owned baris have been to hell and back, and as a result are not much fun to play.
5. Rental baris aren't much better than school baris. And don't even DREAM of using your own horn for this... just trust me on that one.
6. Baritone sax parts in marching bands range from almost-okay, to astonishingly boring. If you're just going to double a tuba part, you might as well learn to play tuba at at least be heard. One guy here on the forum, Saxplayer1004, does this and seems to enjoy it.
7. Given all of the above, tenor will probably have a much easier learning curve, which is going to make it more fun to play. And if you're not AT LEAST having fun, there is no earthly reason to put yourself through marching band to begin with.
Don't get me wrong--I am, first and foremost, a bari fanatic, and I think it would be an awesome horn for you if you already like low reeds. But it's the kind of instrument you can learn to hate in a BIG hurry if your first experience is in a marching band and playing a balky horn. If you want to learn the big horn, do it right... get your hands on an instrument in good repair, and make sure you'll have interesting parts to play. A good strategy for doing this, by the way, would be to march with the tenor (which gets you over the hump of basic sax proficiency), and then audition for your school's jazz band on baritone. My guess is that most high school band directors would practically salivate over the idea of a bari player who could double well on bass clarinet--that's not even taken for granted at the college level.
Anyhow, it sounds like you're already headed toward tenor, but just in case you were on the fence I thought I'd better chime in. Have fun! :mrgreen: