After the tiger and the jaguar, I'm tempted to continue the trend with a dolphin.
More seriously, though, this is a difficult question. Without thinking about this for hours, I'm tempted to say either a sea otter, or a beaver. That way, I get to explore the bottom of seas/rivers, and I get to use tools/build things. Not a bad trade-off, I'd say!
The admin formerly known as Dr. Cossack.
I post musings, images and nonsense on Tumblr! I play games on Steam! Add me on either/both, and don't hesitate to ask if you want to play something with me!
"There are only three things certain in life: Death, taxes, and Teej's obsessions." ~ RisingDragon (still true in 2019!)