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Question can be answered about movies, books or games (and you can argue).
About my opinion :
Books : I, er... don't know actually. I really like both, but they're so different I find it hard to compare.
Movies : Harry Potter, without a doubt. There are events that were changed or discarded from the book, and sometimes that's quite a bad idea, but nothing comparable with the Lord of the Rings. They changed or removed things that weren't just "important", but fundamental. One example (which might seem ridiculous but it actually makes the WHOLE story pure nonsense, even thousands of years before Lord of the Rings even starts) is that, during Elrond's meeting at Rivendell, Frodo leaves the Ring at the center of the room, goes back to his seat, and even lets others touch it. Yes, this simple scene makes everything nonsense. Hard to realize in the movie alone though, as we can't even notice 17 years have passed since Frodo inherited the Ring, it rather seems like it was a few days ago at most.
Games : Barely played to a Lord of the Rings. However, I played several times to The Hobbit. It shouldn't count, but it's the only thing I can compare Harry Potter games to ^^' Still hard since there are several Harry Potter games, and that they're quite different from each other... But overall, I'd say I may have enjoyed The Hobbit more ! (still like all Harry Potter games though. Well, apart from the Deathly Hallows ones... Didn't try them, but don't want to)