Would it be better to put a 3rd place DECA districts award on my common app, or would it be better to put a school accelerated algebra 2 highest average award on my common app?
That’s a tough call - I get it. What is your intended major?
The DECA districts, IMHO, as its a regional award and the school will already see your algebra grade on your transcript.
statistics
I’d put the DECA award. And FWIW I never heard of awards being given for the highest average in a course.