If you had to go with one or the other, I'd get a good treadmill that you can incline at a good angle (15%).
But I wouldn't go with one or the other or even both, because they're very similar in the benefits you'd derive.
My recommendation would be to join a gym and hire a good trainer for 2-3 sessions and follow his/her advice. Because cardio alone won't get you there, you need resistance training plus cardio, especially as you get older.
