Looking to purchase a 40"- 46" Flat Panel HDTV

I think that the manufacturers' ads are confusing you. The sets you are looking at are all LCD displays. The difference is that the "LED" sets use leds as backlights instead of a lamp. This gives much better color and a more accurate picture but maybe not as punchy if you like that. The more expensive sets probably have other advantages.
You might also consider a plasma as these are still the best picture quality and are potentially less expensive in this size range.

Plasma's still have the best picture - I have a Pioneer Elite plasma and a Sony XBR4 LCD and the Pioneer definitely has the best picture on Blu-Ray - deeper blacks and less motion blur (even with the Sony's 120Hz refresh).

However since you prefer LCDs, then I would try and get the store salesman to show the same HD content on your Samsung candidates. If a big-box store like Best Buy, they probably are not going to be too cooperative unless you pretend you're buying a whole home-theater setup costing $10K or more . Anyway, if you're going to bring your own movie to watch, you probably want a recent Blu-ray movie release and not some re-release from the original DVD. For example, the latest Batman movie, the Dark Knight, has some pretty good hi-def and contrasty scenes, both night and day (the office scene with the sunlight streaming in at one corner IIRC). Also, Disney's Enchanted has some pretty good outdoor scenes as well as the ballroom scene. Personally, I just wish they would release the BD version of the LOTR trilogy already, as the DVD has some excellent scenes in it - hopefully the BD version will do full justice to the format .

But each TV you're comparing needs to be optimized for your viewing conditions - the big-box store like to set the brightness way up so as to attract attention. My Pioneer plasma didn't look spectacular out of the box until I set it up with the ambient lighting sensor, etc. But as was said earlier, the LED LCDs will probably have a greater contrast ratio and color gamut that the CCFL models, and since they are the top-of-the-line at the moment, the greatest price and feature list. Besides, that Samsung LED is spectacularly thin!