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All of what Disney-Pixar have released has been instant-classics or instant-classic-level movies. They are infinitely superior. 
Dreamworks has some ok movies here and there. But except for Shrek, nothing comes even close to the catalog Pixar has, not just in terms of popularity but in terms of quality as well. I can probably think of only one Pixar movie that I can say I dislike, while I can make a long list of Dreamworks movies that make me physically cringe, and obviously that I dislike.
But, given that you have not provided any reason other than what you think, it's just a matter of opinion and nothing else.
Talking about Dreamworks and not mentioning one of the best trilogies oat How to train your dragon.