Windows 7 - Which Processor is Better

I'm looking at purchasing another basic computer to have in our downstairs area, like I really need another one, and I've narrowed the choices to a few which seem to have pretty good reviews for our price point $500-$650. My question concerns the CPU which I know is the most important piece of hardware, but gets hard to sort through with the different model nomenclature. Which of the following would you recommend:
Pentium dual core T4300
Intel Core 2 duo T6500
Turion II M500
Anthlon II P320
Thanks for your input.
Brayton

personally i would go for the turionII m500........ but i'm a amd fan. this IS a laptop you're looking at right? the turionII m500 supports hardware virtualization you know

Yes, it is a laptop I'm considering. I'm sorry, but I don't know what hardware virtualization is?

What Is Hardware Virtualization?
this explains better than i could

If you're looking at at laptop, then the CPU is important. What you need to look at is how much power does it use, as this can determine the kind of battery power you'll have.

If you're looking at a desktop machine, then the motherboard is the most important component, as it determines your long-term upgrade choices. I'd rather spend a little more on a better motherboard, and compromise a little on the CPU. Which will be AMD, because experience has taught me that AMD has the best upgrade paths at the lowest cost...

Performance wise, the Core 2 Duo will be your best bet. Cost wise, though AMD will be better, and the Turion II is probably better than the Athlon II.

Core 2 Duo is the best bet as far as performance is concerned and also battery life. If you are going to have it connected to power at all times and performance isn't a high priority, I'd go with whichever costs the lowest amount of cash.

My wife has a laptop with a Pentium Dual Core and I have a laptop with a core 2 duo and mine runs circles around hers on any complex tasks. But for average everyday web surfing and the like, her laptop is just fine and works great.