Both phones are great options, and I would say to look at how you would be using your phone most often. I currently have the Note 20 Ultra and it's a great phone. I would say that if you would be doing work things with your phone, the Note 20 Ultra is made to help you be productive.
The new S21 Ultra is an awesome phone. They've improved every aspect of the phone. If you are a photo person, like me, this would be the better of the 2 options to get. They have improved the camera system on the S21 Ultra even more over the Note 20 Ultra. The S21 Ultra also has a larger battery, at 5000mAh it will last you longer through the day over the Note.
If you currently have a Samsung device, you could get great trade in credit towards a new phone if you purchase directly through Samsung. I only purchase my phones directly through Samsung now because of the great trade in prices they give. And they usually give promotional credits as well, so check out samsung.com when you're ready to make the upgrade!
And to say the S21 Ultra is not a premium phone is crazy, it's definitely premium and worth it.