What is the Best distribution for laptop ???

It is largely a matter of personal preference. Most Ubuntu users with similar hardware are likely to choose Ubuntu 11.04, and that's what I recommend. As for your "flavor" of Ubuntu, the "regular" Ubuntu works very well, and is more widely use than any of the other variants. With regular Ubuntu, you'll have the Unity and classic GNOME interfaces. With Kubuntu, you'll have a KDE 4 Plasma Desktop. With Xubuntu, you'll have Xfce. With Lubuntu (which is not yet an official Ubuntu derivative), you'll have LXDE. It just depends on what you want. You can search the web, and check http://en.wikipedia.org, for more details on all these desktop environments. Finally, since the Core 2 Duo processor is 64-bit, you can run either the 32-bit version or the 64-bit version; I recommend you run the 64-bit version, because it will take better advantage of your processor and RAM.