As an avid HDTV junkie, I have a few things to add. I will focus the majority of my points on LCDs, as that seems to be the current trajectory of the conversation.
Motion blur/artifacts/lag or whatever nomenclature one chooses to employ is an inherent problem of LCD-based technologies, including LED. This 'lagging' is the confluence between two variables that Easy details above: the response and refresh rates of an LCD television set. Before I go on, it may be useful to translate Easy's helpful paragraph into layman's terms.
On the one hand, response rate (RR) simply indicates the amount of time that an individual pixel takes to cycle to and from active and inactive states. RR has been measured in numerous different ways, with the two predominant units of measures being BTB (black-to-black) and GTG (gray-to-gray) - or in other words, the amount of time a pixel takes to go from black/gray to white and back again. While on the other hand, refresh rate simply indicates the amount of times per second the display draws the data from the source: the higher the refresh rate (measured in hertz [Hz]), the more times an identical frame can be displayed before the TV draws new data from the source.
As Easy indicates, early LCD sets often had slow response rates - relatively speaking, of course - that averaged out to 12 milliseconds (ms) or thereabouts. The longer the response time, the poorer the TV performs in reproducing moving images. This is more or less an intuitive concept. As your TV attempts to imitate motion by reproducing a sequence of still images, pixels in different areas of the screen need to be activated or deactivated: if a set's response time is slow, a pixel will retain a portion of the image, and this will create a "blurring effect."
The relationship between blurring and refresh rates occurs under a generally similar pretense. As your TV set draws new frames from the source at a rapid rate to create the illusion of a moving object, it abruptly shifts from one still image to another: if the set is refreshing at a slower rate, say, 60Hz, the moving image will appear to have a shadow or blur. (Which is, of course, simply the still image from the previous frame.) The higher the refresh rate, the more times per second data is drawn from the source, and the less obvious the reproduction of moving images becomes.
Now, choosing an LCD TV based on these specifications, as we can infer from Easy's blurb, is becoming more and more difficult. First, manufacturers tend to manipulate the response rate specification by altering the manner in which it's measured, or refuse to disclose the information altogether. This is a particularly constant practice for lower-tier manufacturers, and to a lesser extent, from top-tier manufacturers releasing "entry-models."
Second, the once-reliable refresh rate specification is becoming quite dubious itself. While manufacturers may list up to 120 or 240Hz, this may not necessarily reflect the true refresh rate of the set. While an actual 120 or 240Hz set has doubled or quadrupled the actual activation rate of the pixels, some manufacturers use techniques such as interpolation or LED-backlight manipulation to reproduce a "120/240Hz effect." Unfortunately, because the measurement techniques for these specifications are easy to manipulate, these 'imposters' are still legally able to list the refresh rate at 120 or 240Hz, though the data may still be drawn only every 30th of a second (60Hz).
Third, and finally, a higher refresh rate on an LCD set may not necessarily translate into a higher performance. As almost any review or technology site will discuss, the higher refresh rate LCDs, while performing well with sports or other constant-movement programming, produce very nasty artifacts with still images. As the same still image is reproduced at quadruple the speed, objects in that scene which are not intended to move at all become unpleasantly sharp. This largely negates the purpose of 120/240Hz TV, as the majority of your content, I assume, will not be sports.
As a result of all this, choosing a lower-tier or 'entry-level' LCD is, in my opinion, generally a very poor idea. Response rates and refresh rates are not often accurately represented at best, and they are manipulated to sell lower-performing TVs at worst. While lower-tier plasma sets come associated with their own host of problems, motion blur and artifact production - one of the most annoying experiences when watching your set, believe me - are not one of them.
Lonewolf,
Out of your available options, I would go with the Panasonic U series. For an entry-level model, it performs reasonably well, and you will not need to deal with blurring issues. If you can, however, I would comb the internet for refurbished G10's (Panasonic TC-PXXG10), as they are last year's model and could be found at a reasonable price.
For reference, I have both LCDs and plasmas. I have two LCDs (an older rear-projection Wega, and 2009's Samsung LN40A650) and two plasmas (Panasonic TC-P46G10 and Panasonic TC-P54VT25 [3D]).