I have the same issue that you have dear and I even asked my personal trainer recently. My trainer said that the elliptical is good because is easier than the treadmill.
She recommended to me to use the elliptical on the days that I do my weight training and the next day to do the hardcore walking fast/jogging on the treadmill .
She also recommended me to work harder on the treadmill because the treadmill works EVERYTHING!!! I need to work on my belly fat and the elliptical is not helping me to get rid of that fat on my belly,however is working great for my arms,legs and calves. Plus I am doing crunches and abs etc. I can burn way more calories at the elliptical and spend 60-65 minutes easily. With the treadmill I can only do 35-45 minutes,but I always put the incline more 5 so the treadmill do the job lol