DDR3 is at the beginning of its life while ddr2 is at its end.
However, currently DDR3 is not that much faster than ddr2. I7 has triple channel ddr3 and Phenom 2's only dual channel, but triple channel is pretty much a gimmick as going from single -> dual is like 5-20% performance increase and triple from dual is even less.
I still prefer ddr2 over ddr3 tho. As I said ddr3 is pretty new so the speeds are barely faster than ddr2. And ddr2 has lower latency. So a program not saturating the entire memory bus will actually be faster on lower latency ddr2 than higher ddr3. Once average ddr3 is 1600-2000mhz then it will justify the extra price and higher latency, but not yet imo.
The performance/speed increase of 3 over 2 is still small. DDR3 is only worth using if you are using at least 1600 speed, and any decent 1600 is 2x the price of good cas5 1066. If you go with ddr2 you can drop 8gb of good cas5 1066 into your build for only 100 bucks. A 6gb kit of ddr3-1600 will run you 150.
Cliffs, if money is no object and you have the cash to burn, may as well go with 3. But I prefer the idea of getting 8gb of ddr2, and then when ddr3 is sufficiently fast to warrant the upgrade, get whatever is fastest then. Chances are you would be wanting to be upgrading the ddr3 you would be buying today at that time anyway, so you saved some money and had more ram in the meantime.
The question isn't just ddr2 or 3 really, but c2q or phenom 2 on ddr2, or i7 with ddr3. I would argue that c2q or p2 plus a ddr2 mobo (as sig suggests i prefer phenom2 platform overall atm) is a much better value than an i7 build right now. Unless you have the cash to throw away.
You can do a 3ghz+ phenom2, top quality full featured mobo, and 8gb of low latency(5-5-5)ddr2-1066 for less than 400. Most i7 920 +mobo combos alone are over 500. A lot more money for a few extra % performance (and basically indistinguishable performance in games, one of the only places where the extra performance is actually needed). Both platforms oc quite well so post oc the situation remains much the same!
You can cheap out on your i7 components and get ddr3-1333 or slower, and a barebones cheap mobo, to cut the price down, but then you are further cutting into the performance benefit and still more expensive than the DDR2 generation build.
Sorry this was kind of off topic, I felt it followed the main one and died into ddr2 vs 3 logically enough to be warranted!
