During a visit to the mental asylum, I asked the Director how they determine whether or not a patient should be institutionalized. 

’Well,’ said the Director, ‘we fill a bathtub with water.  Then we offer the patient a teaspoon, a teacup and a bucket and ask him or her to empty the bathtub.’

‘Oh, I understand,’ I said. ‘A normal person would use the bucket because it’s bigger than the spoon or the teacup.’ 
 
’No.’ said the Director, ‘A normal person would pull the plug.’
‘So, would you like a bed near the window?’
Sometimes when I listen to people arguing about whether the treadmill or the elliptical is superior I think of that story.

Wait a minute…I need to put a disclaimer in here…I am NOT saying that cardio CAN’T be done on these devices, I’m just wondering IF you’ve considered other possibilities.

OK, let’s keep going…
Do you really want one hell of a great cardio session? Get outside, first of all, if the weather meets your tolerances – the same time spent on a bicycle or fast-walking or running out of doors will burn more calories and be more stimulating in so many ways.
Better yet, do a long set of walking lunges, a short set of burpees, a short set of walking lunges and a long set of burpees (repeat as necessary) and I guarantee you’ll be burning more calories and strengthening your core. Or a few series of kettlebell swings and snatches will produce an incredible demand on your cardiovascular system.  Same holds true for  sandbag “shoveling” or TRX powerups, for example.
So, are ya gonna pull the plug on those electric hamster wheels or should I ready your elliptical, I mean bed, by the window?