I have Fox Launch knee pads/guards. They are excellent. Lightweight and are perfect for the type of riding that I do (and by the sounds of things you too). They are a lot lighter and a hell of a lot more comfortable that the more beefy DH type jobs. they feel pretty much like wearing knee warmers. Don’t shift at all and provide decent enough protection. http://www.pinkbike.com/news/fox-launch-enduro-knee-pad-review-2014.html
I recently bought them and was looking at these and ones made by POC, Raceface, Troy Lee, Specialized, Alpinestars, iXS and Seven.
The Fox were on the cheaper end of the scale and lack the impact foam you get with the more pricey options. But were a bit more robust (and unfortunately warmer) than a lot of the other Enduro style pads which I know first hand can rip very easily on harder dirt trails - namely Alpinestars Paragon, Specialized Atlas and Seven Transition.
Thoughts on the others I also liked the iXS Flow, RF Ambush and POC VPD 2.0 and while I liked them, they were overkill for what I needed and that bit more pricey (POC especially - which I guess stands for Posey Overpriced Crap).
Anyways make sure to buy them local as the sizing varies massively from brand to brand and style to style.