"China Clay" covers a number of different chips made at different times by different manufacturers, and they're all a little different from each other. In general the older ones were more chalky and the newer ones are more plasticy. That affects both how they feel and how durable they are. Some (but not all) of the earlier ones are more fragile; the Spirit mold chips in particular have had a lot of reports of being prone to flaking, chipping, and cracking (and in some cases even crumbling). The current generation - the ones imported by Apache and Claysmith/Brybelly - seem not to have these durability issues; they also have brighter colors than the older generation, but the trade-off is that they feel less like a clay chip.
The Dunes and Pharaohs are older than the Royals and Majestics but newer than the Spirit molds and the Tower-and-Spear molds. I don't have any of them myself so I can't really describe how they feel in comparison to the others. I'm sure someone else can weigh in, though.