Hello,

SAT is an entrance examination consisting of section like writing skills, critical reading and mathematics. This exam is for admission in most of colleges in united states. But as you have not mentioned country you want to go and university where you want to apply, it is hard to tell.

Ielts is and English language exam and is accepted by many universities in Europe. Gre exam is also accepted by maby universities.

So it will be best to check which university you want to try or how many universities in that specific country accepts SAT examination and do they require IELTS.