Hi Rawry - all I will say is you really need to try on lots to see what fits and is comfortable but it depends a lot on what/where you are riding and how extreme etc - I ordered about 6 different types/sizes from CRC and most were far too heavy duty and inflexible for regular trail/XC riding - the more flexible (non-armoured) HD lycra/padded type worked best for me and I settled on some Race Face and really pleased with them.
But these are more light protection than real impact stuff.
I have found the ION range to be outstanding for me, top notch construction and fit, and great coverage without being too bulky, and importantly comfy to ride in and dont slip.
I have the knee only version of these, which also have the built in shin guard
I have Troy Lee Designs Shock Doctor guards. I use the knee and shin guards and also the elbow guards (you can get elbow & forearm as well, and just knee only guards)
I have been using them for years. They are not as protective as the armour worn by the DH brigade, but they are lightweight, breathable, stay in place, and are machine washable at 40degC or below, tumble dry at low heat. I wear them all year round and they pull off the seemingly impossible task of not being too warm in the summer, yet provide protection in the winter. Don't guess your size, use the size guide and measure carefully.
I wear them for several reasons. I don't want any more gravel rash thanks very much! They also protect against nettles and brambles. But the main reason is the built in shock protection (hence the name I guess). I have damaged both shoulders by falling onto my elbows and the shock reduction minimises the impact. I also have dodgy knees anyway, so the knee protection is essential for me. Recommended!
Edit: Tipped hat to Mikerb below, "no straps and minimal bulk" is what I should have added to my post in the first place!
My rides are mostly forest trails so not rocky. I prefer self supporting with no straps and minimal bulk. My favourites are G- Form Pro. I have separate knee and shin guards. For stonier ground I use FunKier which are rather more padded but still self supporting and not hard shell type.