I've found nearly any chip is suitable (except for those cheapo plastic chips that are <5c each, but those are worthless for actually playing poker too). Heavier chips definitely tire my wrists faster when shuffling, but for everything else surface texture is the most important. I like the feel of clay better than ceramic, but there's nothing I can do with a clay chip I can't do with ceramic. Obviously minty fresh chips are slightly tougher to shuffle.
Slightly off topic, but after the shuffle, flip, twirl, and knuckle roll what tricks do you learn next? I can't do a table roll or chip bounce, but I'm at a hardwood desk all day where I can't practice those.