Hello,
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Both of them are useful.
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Guess paper is for knowing the expected question which will occur in future examination and to inform guess papers are made from models papers .
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Model papers are useful for knowing the questions which repeatedly occurred in previous examinations and for having an Idea what will be the chances of occurring a particular question in future examination.
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So, firstly go through the guess paper and later refer model papers.
So that if something isn't mentioned in guess paper you can get them from model papers.
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Best of luck