Ooty and coorg both are hill stations and offer amazing views. But the main difference is that Coorg has coffee plantations and an untouched vibe to it. Ooty, on the other hand, is a popular tourist destination. So I think Coorg is better if u want to experience silence and some authentic coffee.
I would say ooty is better as a hill station. Coorg is not a very chill place by itself. Both places are touristy and you need prior planning to get rooms/acco of your choice. The key really is to pick places that are away from the popular places. I have done the same. You can check my blog (www.katchutravels.com) for my review of a homestay in Coorg closer to Nagarhole and of ooty and coonoor, with some trekking trails (also available on my youtube channel by the same name)