Intel® Core™ i3-350M vs i5

no, its not

If you want to get down to the nuts and bolts, Yes the i5 is better.

Although overall, you wouldn't notice the difference.

Questions that are very relevant:
What do you need this for?
Why would you get 1066 RAM for the i5 but 1333 RAM on the i3?

But to answer your question, the main difference here is that the i5 has a slightly higher clock. Otherwise they're quite similar. If this is for gaming, I'm assuming these are simply your options for a gaming laptop... so personally I'd probably go with the i3 since it's probably cheaper, but get a decent video card in there.

I would go for the i3 myself. There are a couple of laptop overclocking programs out there. You could buy the cheaper one and oc it to the clock speed of the i5! Or higher

I'd get the i5. It's noticeably faster when you account for the turbo mode (which the i3 doesn't have).

Those are mobile CPUs. For the most part, DIY laptops aren't worth it.