Which would you pick to lose weight?

So, my new years resolution is to lose weight :) lol

When college starts, I have a pretty busy schedule and have trouble finding time to go to the gym (I'm on campus from 7 am to 7 pm about 5 days a week and my major is engineering so the other 2 I NEED to do homework on.. it's just that much work, no choice).

So I have two choices:

1) Buy a bicycle and go around my neighborhood (It would be stress relieving, but I don't know if it would be enough to lose weight, even if I do it all day)

2) Buy a cardio machine (I want the elliptical) and do it at home any time I want during the day or night (but would this be better option that option 1)

Granted, if I have time I will go to the gym. However, I'm asking this question for the days I can't go to the gym.. like those 12 hour days.

Thanks for your opinion :)
Bicycle
Elliptical (or other cardio machine of your preference, please let me know if so below)
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Updates
+1 y
If I'm not in great shape, can I still do the p90x? I hear people say that you need to be IN shape to do the p90x, plus I have knee problems and bent back bone (just like my dad's family - which sucks because I will probably have back problems when I get old) but I still want to try it, would it be out of my league -- better question.. will I be able to adapt to it eventually?
Updates
+1 y
Thank you guys for your answers! This really helped! I had been thinking about this a while back, but of course finals came into the picture and out went my personal life. I'm going to get the p90x for my weight loss and a bicycle for me to enjoy! :)
Which would you pick to lose weight?
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