There are many models of both of those processors.
Generally, you will find the Phenom IIx4 will provide you with more speed for your money. But their best is not quite on par with the best core 2 quad. If you have more than $200 to spend, the core 2 quad would be more powerful than the x4 at $180. But if you are spending more than $200, it would be better to look at the core i5 series of processors.
A C2Q can use DDR3 on an X48 platform but yes, they should be out of consideration for a new build.. If you are asking for recommendation then you've to be more specific regarding your purpose and budget of course..