Out of all the ones listed I have the Weighted Orgasm balls. They're pretty heavy and I think they're 7/8 inches and I like mine a lot.
The problem I run into is that a lot of the duotone balls out there are rather large for me. Usually around 1.5 inches. If you're able to hold one inch in without even trying then you probably want something smaller.
The smallest set of duotone balls I have is the Luna Noir Beads (they're the same size as the Luna Mini bead, but quieter).They're close to an inch and they're fairly weighty. If you're looking for duotone I would recommend them.
If you're looking for a challenge and want something small the silver balls are 3/4 inch and the Crazy Girl balls say they're 1/2 inch.