I think the general consensus here is the Arcteryx are the best but they are a little pricey. When I 1st started putting all my rig together, I struggled with pulling the pin on the Arcs. I'd already spent a bunch of money on my Kestrel, two Ropeman 1, and other stuff. I wasted a lot of time shopping for cheaper knee pads and I finally decided "what's an extra $20 or so?" I bought them and I'm not regretting it for 1 second.
They do have a hard cap, but they have a kinda tacky coating on them that makes them quiet and sticky against the tree. The thing I like best about them is they are very easy to put on/off. I wear them as soon as I'm leaving the vehicle and, not only do I not realize they are on, they also come in handy for the walk. I occasionally need to get on a knee to squirm under and thru brush. Dead ash trees are creating roadblocks everywhere around here. What was a clear access route yesterday can have a tangle of ash (and other crap the bring down) exactly where I need to walk. Sometimes crawling in the only way thru. Knee pads help tremendously, even if only to keep you pants dry when I kneel. Keeling on snow or wet leaves without pads is gonna make your insulation less effective. And have you ever kneeled on a hawthorn branch or multi flora rose? Get pads that you can walk in and use them.
And then there is the occasional close encounter with deer while walking. You know, you are walking along, and here comes some deer heading your way. Nowhere to hide, right? At least get on your knees and there's a lot less chance of being busted.
IMO, kneepads must be easy to put on and off, and be comfortable to walk in. Arcs fit the bill 100%.