Calories Burned vs. Length of Workout

Has anyone read anything about what is more helpful to losing weight -- the calories burned during a workout or the overall length of a workout?  I use a Heart Rate Monitor and some of my really tough workouts I might burn 400 calories in 3/4 of an hour, but other times when I'm not working as hard it might only be 300 or even less in a little over an hour.  

It seems like a no brainer question that burning more calories is better, but I wasn't sure if duration is a factor, too -- maybe for heart health?  Does one have benefits that outweigh the other? (pun intended! )  

Since I am often pressed for time, would it be better for me to work out hard for 45 minutes 4-5 days a week, or take it easy and get in an hour every day of the week.  Does that make sense?

Thanks for any help!

Calories burned is what matters, however some exercises cause you to burn additional calories after you finish the exercise: http://www.t-nation.com/readArticle.do?id=152 6539

Fabulous article -- thank you!  It totally supports what I have noticed in my own workout experience over the last two weeks.  I was in a nasty two month plateau that no amount of lengthy cardio sessions could seem to bust through.  I had a session with a trainer at a gym who told me to ditch the cardio in favor of supersets and circuit strength training.  I finally lost 5 lbs in the last two weeks because of it!  

The article really helped solidify this new routine for me.

Hi stewmama,

I read the article too and I didn't understand what they were saying to do exactly... and I'm wondering what you did to get out of your 2 month plateu??  I have also been in a 2 month plateu, and I am still in it and I don't know how to get out! 

So what did you do to get out of it?