I'd probably go with the AMD combo. The 6300 won't be as fast in game clock for clock as a stock 3570, but the motherboard with the 6300 is much better and you can use that to overclock the 6300 which will help a ton. Also, you will be able to upgrade down the line with the AMD because there is still one more line of chips to come out for the AM3+ socket.
Well, in this case, yes, the 3570 clock for clock is better than the 6300, but when you factor in overclocking and price for performance, the AMD option is the better way to go. If you want something that'll perform just the same, if not better than a 3570k, then get an 8350.