OK, I'm an AMD fan, but the 4200+ seems to be at least a reasonable alternative to the E6300 for the average user, at that price point.
AMD Athlon 64 X2 4200+ Retail $182.00
Intel Core 2 Duo E6300 Retail $182.00
To add even more insult to injury the slowest Core 2 Duo in the test, the 1.86GHz E6300 is barely slower than AMD's fastest Athlon 64 X2.
The processor landscape has been changed once more thanks to AMD's extremely aggressive price cuts. The Core 2 Duo E6300 is a better performer than the X2 3800+ but is also more expensive, thankfully for the E6300's sake it is also faster than the 4200+ and the 4600+ in some benchmarks. Overall the E6300 is a better buy, but at stock speeds the advantage isn't nearly as great as the faster Core 2 parts. In many benchmarks the X2 4200+ isn't that far off the E6300's performance, sometimes even outperforming it at virtually the same price. Overclocking changes everything though, as our 2.592GHz E6300 ended up faster than AMD's FX-62($695.99) in almost every single benchmark. If you're not an overclocker, then the Athlon 64 X2 4200+ looks to be a competitive alternative to the Core 2 E6300.
*** I added the $695.99 price tag for the FX-62, thats the current price for it VIA newegg.com
Remember NOW the E6300 and the 4200+ are the same $
The E6300 and E6400 can easily overclock to E6700 and Core 2 Extreme X6800 levels, though the smaller cache does limit performance a bit. That being said, our overclocked E6300 was able to equal and in all cases but one outperform AMD's Athlon 64 FX-62. In fact, in quite a few benchmarks, the overclocked E6300 is essentially out of reach of anything AMD can offer with their current K8 designs. At $182, the value here is tremendous, and if you're willing to overclock the benefits don't get any clearer than that.