Ugh..good luck with that decision!
I'm kinda in a similar situation. My school offers a 4+1 program, where I can stay there for another year and leave with my Masters degree. But I still have to decide whether I should do that or just go into the teacher profession with my BA and then go back to get my Masters in a few years. It really depends on the job market and how the economy is looking. For teachers who only have a BA, our starting salary is lower, so that might make me more marketable to places hiring. Maybe they can't afford to pay me a higher rate, which would be the case if I had my Masters, so it would broaden my area of prospective jobs.
I have to go out and talk to a couple schools/superintendents to see how they feel. That's just my logic, but I need a professional opinion before I make an decisions. I apply for the program my senior year, so I still have some time to think about it more.