Some single colored marbles are, hand-gathered CAC Pastels or World's Best Moons, German Opaques, some Master Cloudys or Akro Flinties, maybe. As for other types, I like the Vitro Tomatoes or others with exceptional patterns. A lot of it just depends on what you like. Typical game marbles have little if any collectible value though, so I wouldn't expect to get any money out of them, which means you could just keep them in a jar, play with them, donate them or do crafts with them, because it's not going to "cost" you anything to keep them either. 🙂