For 16T or smaller I'd recommend Dura Ace, which will cost between $20 and $25 depending on where you buy it. For 17T and larger I'd recommend Soma, which in black will cost less than $20. And yes, the stock cogs are pretty bad, not very round or well machined. Even the one that came on my more expensive Kilo WT was pretty bad, and it sounded like it was full of gravel. Chain tension was pretty uneven on it as well. As soon as I changed it, the drivetrain became silky smooth and quiet and chain tension was very uniform.