If possible demo them side by side with the same copy of a movie you like or any movie with good fast action scenes (to test for motion blur) and some good dark scenes (to test for black levels). It would be better if you could demo the movies at the same time, same scene, side by side with identical presets.
The TCL one might be at a little disadvantage side by side in terms of picture quality (if they have the same resolution) since it would have a bigger screen. So you have to keep that in mind when comparing.
If you don't plan on using external speakers then you should also test volume levels and clarity, although it will be harder to gauge since you will most likely be in a showroom.
You should also consider comparing warranties, extra features and bundles like free flash disk with movies or discounted HTIBs.