I really like your question! I would have to say space without second guessing!
When I’m imagining myself in both situations, space is ideal for me. I’d be able to observe infinite sceneries while floating around. Stars, other galaxies, comets, real natural minerals, stardust, crystals, astroids, other planets, other moons and supermoons, other suns, all different beautiful natural colors and sparkling twilights, and so much more.
The thought of floating at sea puts my state-of-mind in a place of endangerment when compared to floating in space.
Sharks, piranhas, killer whales, stingrays, jellyfish, and any other dangerous and wild creatures of the sea, I would prefer not to be anywhere near their vicinities. I’d feel more lonely floating in water with hardly anything around me to attract my attention of interest. There’s not much to see at sea that would inspire my imagination to run wild.
I can only gather accounts of unwanted trouble floating in such a massive body of water. If I wanted to observe anything exciting and/or beautiful, I would have to swim to the bottom of the sea. I wouldn’t be up for such an adventure. I’d be too frighten, focused only on me being harmed, drowning, or in some type of dangerous situation that I wouldn’t come out alive.
At least if I were floating in space with the possibility of not making it out alive, everything else would be floating as well. At least I imagine nothing would forcefully be coming my way that could suddenly hit me and cause me injuries.
Floating in space is definitely my kind of adventure. I’d rather be the company of the many things outer space versus the company, or possibly dinner, to the many things at sea.
I’d also be a whole lot less likely to be kidnapped in space than at sea.