I have a bike and a treadmill. The treadmill lives in the garage now - it was a PITA because it folded but since the running bit lifted it had to be facing the wall for the folding to minimise space. I just can't cope with staring at a wall while I run. If I'm going to run indoors I need stimulation. Turning it around so it faced the TV meant that it took up heaps of space and I had the wall right at my back so in the event of me tripping on a lace (not likely but I'm a paranoid Polly) I would have been thrown straight into the wall - it kinda made me feel claustrophobic being jammed between the wall and the front.
The bike on the other hand doesn't take up much space and I can face it towards TV so I can watch TV while I work out.

I tried out a few cross-trainers but to buy one that felt really stable cost heaps more than a bike of a similar quality.