You don't have anything to lose besides some time unless you wanna play another sport during either season. I recommend training for the 800m cuz it'll make you tough mentally and physically, but that's just my own bias talking. Our school only has track, but no XC and I could tell you the difference XC would make on track season and vice verse. One teaches you to run at an uncomfortable pace for a long time, and the other teaches you to run fast for a relatively short distance. They are complementary to each other, meaning improvement in one can lead to improvement to another. On another note, I started running track to get in better shape, figured out I was half decent at it, and now my competitive spirit makes me love running, so try both out, and who know maybe you'll be like me and learn to love such a painful sport