We got in a boatload of (as in a couple hundred) Ergotron arms here at work... Almost all of them failed within a year.
No idea what their quality is like these days, but they used to be overpriced junk.
I bought an AllCam GSD at home for myself and for the past few years it's been frequently repositioned, but is as solid and precise as the day it came out the box. Pretty cheap, too. Highly recommended.
Screen size is probably less important than the monitor weight, as overloading the mechanisms on these things is what kills them quick. If you're getting a fancy, lightweight Asus sort of thing, then you're probably cool, but DO check first!
