<p>Every college now accepts either the ACT or the SAT without prejudice. Your 34 ACT is outstanding. Go with it. A small number of colleges will want you to take SAT subject tests whether you take the ACT or the SAT; most will accept ACT with writing in lieu of both the SAT Reasoning Test and SAT Subject Tests, but you should look at the requirements for particular schools you might be interested in. </p>
<p>You already have a 34 on the ACT (99th percentile) as a sophomore. You could try to improve it to a 35 or 36, but frankly, most colleges are going to treat a 34 the same as a 35 or 36, so any marginal benefit will be slender.</p>
<p>An 1800 on the SAT is a pretty good score, well above average, but at the 82d percentile it’s nowhere near the strength of your ACT score. With work you might be able to improve it, but the question I’d have is, why bother? You’re better off concentrating on SAT Subject Tests and nailing those.</p>