I like the transluscent wave ones. I've never been able to decide if I prefered the multi-color waves or the mono-color waves. I voted single color, though.

Looking back, I have no idea why parents would let their children play with marbles. I mean, tiny glass orbs that you flick and ricocheted around at high speeds? And playing "for keeps"? Yes, that's right, give 'em the passion for gambling good 'n early.