The two are almost identical. The (very minor) differences are mostly about what you’re planning to do with the degree. He should choose LAS if he thinks he might want to teach, maybe if he knows he wants to go to grad school for theory. Engineering might be better if he doesn’t plan on going to grad school as it’s probably a bit more marketable to employers. I’m in Specialized Physics in LAS, which is basically the grad school track. It’s a bit more focused than the Science and Letters program, so be aware that there are multiple options in LAS (the teaching track is also an option.) There are some differences on the college level. If he didn’t take four levels of foreign language in HS, he’ll have to take more when he gets here if he’s in LAS, since we have to have four, while Engineering Physics majors only have to have three levels.
But in all reality, everything is in the same department and it’s not that much of a hassle to switch if he ever feels the need. Most of the people I know literally just chose whichever one sounded cooler to them.
As a side note, however, don’t count on merit scholarships from here just based on ACT and GPA. I graduated with a 4.00 (my school didn’t weight) and a 35 on the ACT and didn’t get a dime in merit, it’s very competitive.