There's no possible way by which someone can love Oasis but dislike the Beatles. If you've seriously heard Oasis or ever read sth about the Gallaghers then you'll know you actually suffer some kind of schizophrenia.
Anyway, don't dare to say they're the best british band ever, but they are undeniably huge and, in my opinion, a little bit underrated. For the one who said they are only big in Europe, lad you outta come down here, South America for instance, and realise u r wrong. Not many bands can come play to thousands and thousands of people in a football stadium in Brazil or Argentina almost 20 years after their debut. They are legends.