Is it better to use the treadmill/recumbent bike for longer time period (longer miles) with less resistance or shorter time period (less miles) with more resistance?

Well, I think there's been a lot of study done in this area - whether or not you are working in your 'fat burning zone' and so on. From what I've read, the longer you work out, the more calories you burn, even at a lesser intensity (Of course, you don't want to be just meandering!)... and since weight loss is, basically, calories in versus calories out - well, you see my point.

I do know that new guidelines have been issued suggesting that 30 minutes of cardio three times a week is not enough to lose weight - the new suggestion is 60-90 minutes three to six times a week! Gives you an idea, though.

HeatherAngel -- where did you hear that?!!?? ah!

It's the new government guidelines, but you should work yourself up to 60-90 minutes... Starting at 15 minutes is better than nothing when you are a beginner....

There have been recent studies showing a greater fat loss with shorter, more intense cardio done in "intervals" (moderate intensity with periodic sprints into the high-intensity zone). This results in EPOC = Excess Post-exercise Oxygen Consumption, which means that your metabolism is elevated for hours after you're done exercising and you continue to burn more calories.

I used to do an hour on the elliptical every day at a lower intensity. Since reading more about cardio and fat burning, I do a half hour but at a much higher intensity, with intervals. And I'm very happy with the results. So my vote is for shorter time and more resistance.