The numbers go like this: 1st number is the number it writes at, 2nd number is the speed it re-writes, and the 3rd is the speed it reads at.
As for the bigger the better, yes the bigger the numbers the faster it writes, re-writes and reads cds. You will definately want something faster because it takes a long time to write things at 2x compared to 12x, I know this from experience. But as far as what JTang said about the quality of the cd, I think he may be right about that. Because lately, after we got the 12x, my cds have been scratched up very easily, and my portable cd player can't play them very good, although I think that cd player is messed up. But I think he is right about the quality being effected by the speed. But it sucks having to wait for the cd to finish. But I have an Iomega 12x4x32 burner and it does pretty well.