I use a number of different light boxes at work as we use them for inspecting materials. I really don't find one brand vs another to make much difference. I have a small, inexpensive Testrite (9.5" X 12") in my darkroom and feel that it's a good compromise size. The space that I have for it is small so that I wouldn't like the intrusion of a larger one but it seems adequate for holding the typical array that I'm dealing with. I imagine that if one was laying out publications, etc, a larger size would be more sensible but for my home darkroom duties, I'm quite pleased with it.
As an aside... there is a tube glow to it that takes a minute or so to dissipate. I've not felt that I'm getting paper fogging from it but I have it placed where it isn't likely to have much effect. This could be a factor in the right circumstances.
I'm moving my darkroom into a larger room and am considering building one into one of the work surfaces. I use one in the lab at work that is made this way and it's handy to use it as added table area but still be available for viewing when needed. Also, if you buy a commercial one, you'll notice that they have a movable top mount that allows space to add a layer of glass to protect the top. This is handy as it cleans up nicely and allows a surface for cutting tracings with a razor blade, too.