You can say - for example -This is the best paella! meaning that you think it is really good (en español= que riquisima??) It may not necessarily mean that it is the best paella you have ever had, but you think it is really delicious. If the paella is the best you have ever had - say 'This is the best paella I have/I've ever had/eaten'

"This is the best" means "there is nothing better". If you use this term literally, then best means better than great, because something could be "great" but not "the best". So if you use the term "the best" then it literally means there is nothing better than the object you are referring to.