i was going to type out everything but i found another link that sums most of it up here;
k20z3 engine breakdown - K-Series Forums
hope that helps somewhat. if his budget is around 15k he would probably find an rsx-s a lot quicker than an si, but correct me if i'm wrong. and i didn't say anything about the quality either. i remember seeing a type-s on craigslist for 9k, but it had tons of miles on it.
personally, i'd go with the civic just because i like how it looks a little better. a red one thats lowered with a lip kit looks pretty badass. honda's still producing new ones so there will be a lot more aftermarket parts coming out.