Hi! I have never personally owned a water dragon or a bearded dragon, but I do work at a pet store where I kind of own them! And what I can tell you is, they get huge and require a lot of room. Chameleons will also end up needing a bigger viv, but it will be taller, not a giant 75 gallon long. Chameleons may end up needing a lot of special care, like vet visits. (I have two.) Leopard geckos would be the easiest if you wanted something simple and small, they stay pretty small and don't require too big of a tank.
So,
Beardies: big tank, big reptile, but they are so calm and loving and will just sit on the couch with you like a human, but require certain housing
Water dragon: really big so really big tank, really skiddish, and require a lot of humidity
Chameleon: fun to watch, funny personalities, but do require more intense care
Leopard geckos: easy housing needs, stay small, cute little faces, but still are rather squirmy
If you do choose one of those, please just make sure you read up on it before you get it even if I made it sound easy! No reptile is 'easy' to take care of, some just more simple than others. I hope I helped!