The short version is active is more detailed but passive can be more comfortable. The comfort of an active TV seems to be tied in to the motion performance, when I was looking last year the ES7000 and HX8 were super comfy to watch in active, but the lower down the range actives were not.
Passive sets you have to be carefull about the hight of your tv (think mounting above the mantle piece), if you are looking up or down at the tv at all in won't work properly. You can fix this with angle wall mount brackets.
If you are looking at a midrange set go passive, if you are looking high end go active would be my advice. (Actually, my advice would be dont pick a tv based on 3d preference because you will get bored of it after two films, but that's just me
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