In terms of raw computing power, the two systems use similar parts, and will have similar performance.
The benefits to going with the M1330 are smaller size/weight, better design (like the touch-sensitive media keys), appearance, and option for a backlit LED display. The drawback is that you're going to be paying for that design and miniaturization.
If aesthetics, form factor, and the option of an LED-backlit screen (it's a NIICE screen!) are worth paying a few extra dollars for, then the M1330 is one helluva sexy laptop. If you're looking for the best bang-for-your-buck and are willing to sacrifice some of the benefits of the M1330 to save a few bucks, then go with the 1420.
Personally, I'd go with the M1330. A year from now, you would have long forgotten about that $300 that you would have saved, but your laptop will still be something that you interact with on a daily basis.