With a lappy I'd go for the most powerful processor available when you buy, cos they're pretty difficult to upgrade. I'm not entirely sure which of those is most powerful but I'd put my money on the i7-720.
I have the i7 720 in my alienware M15 and i have to say i am totally impressed with its performance.
Its way over the top of anything i have ever used before, I generally multi-task alot, using anything up to 3-4 programs at the same time and probably up to 10 webpages open too and i have not seen the CPU usage above 20% and never had it hang or slowdown.
As you can tell i'm a big fan of the i7, hope thats helpful in someway