I don't know the difference between Bitcoin Core and Knots, and at this point I'm afraid to ask. 
Discussion
Me too 🫂
Knots is mostly core with a few extra features. One big difference is optional filters for some types of spam. More flexibility and a focus on bitcoin as money only.
Core is planning to remove spam filters and bump up size of op_return to allow more arbitrary data to be included with transactions. Knots will add these the filters back in and keep the smaller op_return size.
There are a few debate videos that give a good insight into the view of both sides.