My personal favourite is matte paper Micarta, it 'feel' warm in hand. I have a feeling that any non-natural material once polished may probably feel 'slippery', and a matte finish might reduce that chance.
Canvas micarta for function (not quite as wear resistant as G-10, but not as sand-papery in the hand either), wood for looks (and it feels just so right in the hand). I sometimes opt for synthetic handles when the only wood options are obviously not sustainable. Too many hardwoods are close to extinction. A knife handle isn't much, but it's more than nothing.A lot of scandi knives have (un-stabilized) birch handles. Soft, not wear resistant, but it doesn't crack (i.e. less than many expensive types of wood), they don't get brittle in low temperatures and the ergonomics are just excellent.I'm the first to admit I choose knives both with my brain and my heart.