Samsung, LG, Viewsonic, DELL , HP they are all good LCD brands (don’t know about Megabox though). You cannot say a particular brand is better overall than the other, without comparing a specific model number. Because it all depends on the panel used in that particular model. Sometimes a specific Samsung model can have a better panel (colors/ contrast/ viewing angels) than a specific LG, and if you compare a different set of models LG might turn out to be better. So you can't really say. But given a choice a reputed brand like Samsung and that unheard Megabox or whatever, I'd say Samsung.
As far as the monitor specs are concerned look for the following :
Response time : the speed which the pixels can change color (black > white > black), lower is better i.e : 2ms is better than 5ms. With longer response times like 8ms you can sometimes see ghosting or a trail of light left behind by a fast moving object (especially noticeable in games)
Contrast Ratio : Usually the difference in the luminance (brightness) of the darkest black and brightest white. Higher is better i.e : 1000:1 is better than 500:1. With a high contrast ratio you’ll see rich color contrast (deep black colors)
Viewing angle : This is the maximum angle at which you can view the monitor without noticing lot of color distortions. Higher the better
If you can compare working monitors side by side, then that is the best way to choose, otherwise you'll have to rely on the specs or someone else’s experience.