Hard to tell without seeing the rest of the room

Depends on if you want you would do with the mantle. Pictures, kids Christmas stockings or other decoration. Or do you want a nice decorative statement piece above your fireplace.
Because I like options, and there's so much you could do with a mantle, I'll vote mantle. But if this is to be a chic, grown and sexy house, then disregard my vote, and go decorative stone wall.

I have a similar fireplace to yours. It was originally coal burning and I put in an insert that looks like the real thing. I like contemporary, but I think in your situation with the small fireplace in a big room in wouldn't look right. My room is probably much smaller than yours (14 x 14 feet) but the ceiling is high (11 feet).

These pictures will probably post sideways or upside down. Apologies. Since the changes happened on houzz this has been happening randomly.

Stone all the way up will add drama