If your ultimate goal is to become a USMC sniper, would you be better off to take an infantry position as a rifleman (MOS0311) or an assaultman (MOS0351)? Does it make any difference at all?

It really doesn't matter, though an 0311 would probably give you more of an edge. Just by the virtue of handling a rifle more and being exposed to light infantry training and tactics more so than an 0351. However, the scout teams will still come around and 0351s are just as likely to be recruited as 0311s. Then you just need to pass the tests.

Thank you for those observations. It was very helpful and I passed them on to the person trying to make the decision.