What are the top grading websites used in schools today? For example, Infinite Campus and PowerSchool. My current school utilizes Infinite Campus while my previous school relied on PowerSchool, so I believe those are among the most popular options. What do you think?

Both Infinite Campus and PowerSchool are indeed among the most commonly used grading platforms in schools across the U.S. Here are a few other popular options that you might find useful:
The best option often depends on the specific needs of the school district, as well as what features teachers and students prioritize. What features do you think are most important in these systems?