Just depends. For example let's say you have a Sony Bravia (which I have) and then you play it at your friends house and he has a LG it may not look as sharp because of the make and other various reasons. Some are TV adjustments, cables used (component, composite, S-Video, HDMI, etc.) and mainly the quality of the screen.
If you are not using component cables do so then you might want to check your TV settings. I notice if you use the Edge Enhance 2 (or whatever it's called. I'm not getting up that TV is in the other room) on WEGA TV's it is too much sometimes, so I set it to Edge Enhance 1. Yes, using the progressive scan is always better then interlaced. So set it to 480p as opposed to 480i.
I hoped this helped you out some.