I think you mean, Which is best Core 2 Duo or Cor 2 Quad? Answer: Depends on your usage and price point. The quads are more expensive for sure, and may only offer marginal performance gains over the core 2 duo depending on your usage. If price is not a problem, or if you run video editing or rendering software I would tell you to buy the Quad, as in the future applications will be better able to take advantage of multiple threads. If you are a normal user a Core 2 Duo will do fine.
the Intel core 2 quad
The quad core processor has four cores. It is essentially two of the Core 2 Duo processors as the Core 2 Duo only has two. The quad core will be faster and as a result more expensive.
i think cure 2 duo is best
To be blunt, the Core 2 duo has two proccesing cores while Core 2 quad has four proccessing cores.
core 2 duo e-series best motherboard
From an AnandTech article the answer appears to be 582 million transistors for the Quad, 291 million for the Duo. Reference: http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2866
The Intel P45SG can support the Core 2 Duo and Core 2 Quad, and is an all-around solid board.
Since the core 2 duo processor has two execution units, it can execute two threads simultaneously. (If you said quad instead of duo, the answer would be four.)
The Athlon x4 will be better as it is a quad core compared to the Core 2 Duo's dual core technology. Should you wish to look at the Core 2 Quad, then the Core 2 Quad would be a better choice.
There is no difference between dual core and core 2 duo. Intel just name its recent family of dual core processors as "core 2 duo". Both (core 2 duo and dual core) works in same fashion.
Intel core 2 duo
In a competition, a solo team has 1 member, a duo team has 2 members, a trio team has 3 members, and a quad team has 4 members.