I think PVC is superior in every aspect other than weight, and MAYBE heat retention. PVC is also mildew resistant. I don't have bearded dragons, so I'm not sure if that's an issue or not, but if a water bowl gets knocked over, you don't have to worry about it. Melamine, you have to seal or at least paint the edges for it to look nice and uniform. PVC is the same color throughout, so cut ends look the same. It's super easy to cut, drill, glue, and put screws in. Like you said, the weight is a big factor on it's own. 1 sheet of pvc isn't light, but it's manageable for one man to move around. 1 sheet of melamine is a different story.