For knees, 661 Kyle Strait knee are excellent, comfy and very protective. A wee bit sweaty but not badly. When you see them, they look a bit enormous and "extreme" but that's why they work- small pads tend to be uncomfortable, big pads have room to move.
For elbows, I'm not sure… I wear 661 Chicken Wings but they're sweaty and slightly restrictive, I'm not all that impressed with them. Just got some POC Bones, which are a) expensive and b) look like I'm auditioning as an imperial stormtrooper. But they're comfy and much less sweaty, and have a lot of protection. They're supposed to be one-size-fits-all but they're slightly too big for my pipecleaner arms.