I'd suggest you read some of the 3D threads to learn some of the pros and cons of each system (active vs passive). Then you'll know what to look for when you go and see them in a store. You need to see for yourself, obviously, and not take anyone's word for it.
This subject has been covered over and over again, but to my mind, the important cons of active are:
- Expensive, battery-powered glasses (though they're getting cheaper).
- More crosstalk with active.
- Significantly dimmer than passive.
Passive has its own drawbacks:
- More prone to moire. (That shimmery effect as with, for example, a patterned shirt).
- Prone to stair-stepping with sharp sloped lines.
- Loss of resolution, of course.
All of the above drawbacks to passive will be affected, to a greater or lesser degree, by viewing distance. That is to say, it will make them more or less detectable.
Personally, I have a 65" LG passive 3D set and I think the 3D is quite good. By the numbers, the resolution equates more to 720p, but it seems a bit better than that. Although I don't really buy into the "image fusion" argument.
OTOH, I also have a 70" Sharp. Since Sharp uses the active system for their 3D sets, I got the non-3D model. Sorry, I don't like active, but that's JMO.
Nevertheless, the big Sharps offer a pretty good 2D picture for the money. And if you want active, I'd have a look at them.
Good luck whatever you get.