Another vote for Versafine (Onyx Black) here. I did a try out of various inks on silhouette-type stamps on my blog
recently, and Versafine gave the best solid image. These were just inked up( ink pad to stamp) and stamped as normal (card on desktop, then stamp to card)). As you found, Distress Inks don't do well on this type of stamp, and Memento only fared slightly better. Can't comment on SU as I don't use their products. As some others have said, a good, smooth cardstock is essential, and another way of preparing a new stamp is to go all over the surface with some low-tack tape. It will take off the slightly powdery residue from manufacturing. Some people also swear by having a surface with a little 'give' in it to stamp on-mousemat, newspapers etc- but I have always preferred a solid surface.