That's a bit of a difficult question.. You see just going by the specs you see on Newegg won't tell which Chip is better/more efficient/whatever. There are many variables to be taken into thought when judging a CPU that just aren't provided to you, even on as useful a site as newegg. Pipeline length, Efficiency of the specific architecture, and IPC (instructions per clock) are just some of the terms thrown around that could shed light on your conundrum. However this knowledge is still alittle hard to come by so I'll give you the scoop, layman.
Short pipeline length, high IPC, and A solid core architecture (especially with overclocking)make the new Core2duo the most powerful chip you can buy right now. The AMD X2 lineup is just slightly behind C2d, they are beaten in benchmarks but most of the time the difference could not be noticed in reality. Behind them are core duo, Pentium D's, Athlon 64's, Pentium 4's, etc, etc.
It's alittle hard to explain it all, if you're have any questions feel free to ask them.. My best advice to you being google! Use it to find benchmarks to gauge chip performance, or whatever.