Which one is better? The Athlon. Even though the E1200 is based on more efficient Core2, the Athlon's got 4x the cache and an integrated memory controller which gives it a massive performance advantage over the 1200 in games and/or multimedia apps. In everyday tasks they'll probably perform the same.
Not sure I know higher models Intel creams AMD far as overclocking/cache goes but I can't tell a difference between a 9950 @ 3.0ghz and a Q6600 at 3.6ghz in any games I played on (friends PCs)
I quite love my X2 4400+...cheap and high quality I don't like to OC but friend got his to 2.9ghz. Runs Farcry on High on Dx9 and Medium-High on DX10 (have to turn shadows down on DX10)