I prefer the overwater shot but I like both of them for different reasons. I think Overwater gives a better, more natural looking photo. I like that you can see a bit more of the hills in the background and more of the tree/shrub thats growing on or behind the rock.
The underwater shot would be cool if there was something under the water to show like fish or other cool flora/fauna and you do get some interesting background shots of that rock with the red in it and the snow capped hill/mountain on the left you couldn't see with the overwater shot.
In both shots I just have to say how AMAZING the blue sky looks. It really contrasts with the brown and green of the water below it and it pops out at you. I'm in Washington state so its fairly rare that its as blue sky as I'm seeing so maybe thats why I'm excited over it. I'd show a picture of my sky but it would look like I just took a photo of some drywall.