I've worked up during the past 4 years from cheapo discount shop pads to my current unbelievably bulky "187 Killer Pro" pads ( http://187killerpads.bigcartel.com/product/pro-knee-pad-black-black
) . These are intended for roller derby and half-pipe/bowl skaters. They have 40mm (1.5") thick foam, so as the derby folks are keen to say, "It's like falling on kittens". After smashing my knees through a variety of half-assed pads in the past, these are the first pads I've tried that will take a one knee landing without any pain or damage whatsoever. And no, they don't get in the way. Though they did a little whilst learning backward crossovers, but i'm not jumping or spinning seriously yet, time might tell.
Knees pads sadly have the same basic physics limitation as helmets, and that's that thin foam simply CANNOT protect nearly as well as thick foam, no matter how high tech the foam is. D3O is good stuff, but it can't repeal "F=ma".
Of course, I don't expect ANY figure skater in the world to be happy wearing such bulky knee pads. But if avoiding pain/damage is essential, these are the only style of pads that will do.