Read the first book of each series and see how you feel about them. No need to commit to the whole series until you're sure you like one. Both are great in their own way. But it is worth noting that Dune gets really different after the first book and books 3 and 4 of Hyperion are like a whole different story. You might consider reading the first book of Dune, then Hyperion and Fall of Hyperion. Then see about the rest.