The Core 2 Duo is the undisputed king of mobil CPU's right now, but you have to watch out which "model" you get. It isn't as easy as just Core 2 Duo.
The AMD X2 Turion dual core is not a bad CPU, and with the new AM2 platform MAY be upgradable to the next gen of chips the 4x4 Quad Core which AMD
should regain the upper hand.
The X2 runs a little hotter, and uses more juice than its Intel counterpart.
Many times it is hard to find an X2 with a decent GPU in it, that is one MAJOR drawback AMD has. An nVidia 7600 or x1600 is probably the best you are going to do right now, maybe an x1700.
Since Intel and AMD are both 64 bit (Core 2 Duo) that really isn't an issue anymore. So it comes down to
:arrow: Budget
:arrow: Overall system build quality (check the LCD, Keyboard, Chassis etc)
:arrow: GPU desired with the system
:arrow: Personal preference
:idea: If it is between a Core Duo and an X2 go for the X2, the core duo's are 32 bit and have a slower fsb than either the C2D or the X2 (by far on the X2).
:idea: If it is between a Core 2 Duo 5xxx series and an X2, go for the X2 (The 5xxx series of C2D do not have the 4 MB cache and have abismal clock speeds).
:idea: If it is between a Core 2 Duo 7xxx series and the X2, go for the Core 2 Duo (4MB cache, plenty of clocks, manhandles the X2 in any and all benchmarks.)