I've had this problem a lot. In the past I've been a gym member, had a few exercise videos at home, had bike at home. I stuck with the gym thing better than I expected, I think about 3 months or so, but really found that I dreaded going (I think it was a lot of a social issue for me, I did not like working out in front of people).
Lately I think I've found a sliver of success in the WATP videos. They are a lot of fun for me, and I've been doing them at least once a week (which is seriously an accomplishment for me) for about 2-3 months now. I found with a lot of the other cardio videos, not only was I so poorly in shape that I found either my lungs or my chest aching after so long, but the coordination required really discouraged me. With these I get such a boost afterwards (and it's nice to warm my body up in the cold weather
).
I think it's really about finding what
you enjoy the most. And that's different for every person. Like the gym for me, was too socially intimidating and when I realized that was the biggest reason I didn't want to go, I slipped into the comfortable schedule of working out at home and that was much better. Anyways, I hope this helps, just my 2 cents.