I agree with corbeau. If you can, go with Piledriver above the 2 the two bulldozers you have chosen. Either the 6300 or 4300. Bulldozer just has too many issues, of which many were sorted out by the time Piledriver released.
If it's between those two, get the 4170. It's a little more powerful than the 4100. But if you are buying them from a store, get the 4300. It's better than both of them.
What is the background here? Someone giving them to you? Are you gaming?