I have to agree with Mark on Hahnemuhle Photo Rag Pearl. I preferred Hahnemuhle Photo Rag Baryta initially but they seem to be able to make the Pearl roll after roll very pristine, I had problems with flecks in Baryta. Performance is great, some of the other PK papers mentioned have more gloss differential than Photo Rag Pearl. I've gone through a lot of it for a few clients and it's been great. The other PK paper I like is Cone Type 5, a bit more texture than HPRP and a bit warmer.
For MK I like William Turner and German Etching for personal work, but for others the delicate surfaces are difficult to deal with, I can't control how others handle the prints. Canson's Edition Etching is very good too, and for those who prefer a neutral smooth paper I use Rag Photographique with no problems. I don't really prefer smooth MK papers myself, they feel too card like to me, but for others Epson Hot Press Natural performs very very well if anyone prefers a bit more base warmth that Rag Photographique. I just completed almost 400 prints for a Kickstarter project that the signature series coatings made look great with their big gamut and dmax, so even though I think the Cold Press surface is a bit "manufactured", I used Epson Cold Press Natural for the entire project and was very impressed. Since there would be a lot of handling of the prints by less than experienced people the more robust surface (compared to William Turner) was the way to go. Edition Etching would have been a nicer surface, but when I saw the color and densities on the signature papers I couldn't give it up.
Tyler