-Honestly, the temptation of time travel is almost too great to pass up. But, I would likely mess up things worse than I have them now. -Biologically immortal is tempting too. However, you would watch a lot of people whom you care about pass away, so it's more of a mental and emotional struggle. Plus, if you live long enough something bad will likely happen to get you killed or severely injured. -Could you swim as deep in the water as you want (i.e. withstand as much pressure as you want under the water)? Vision might be a problem with very powerful lights. But, "Aquaman" is interesting/fun. -I guess boring money is the safest bet to me. It is a lot of money, so maybe I could do something benefi... who am I kidding I'm blowing on the frivolous stuff.
Biological immortality, oddly enough. The idea of watching friends and family grow old and die while you remain young may appear dreadful at first, but when you factor in how we can get attached to relatively short-lived pets as if they were family - down to even taking on a patronage of a pet's lineage - it becomes entirely feasible that such an immortal would develop a similar relationship to their mortal kin. Couple that with all the time in the world and some careful planning, and money ceases to look like an issue. I realize that this sounds a lot like how a vampire would spend their time when not looking at people like they're gushers.
Yes... let's assume you had no issue with the pressure... we'll even throw in the ability to withstand the cold (just to help even things out). Basically you're as comfortable in the water as a fish (but obviously you can't swim as fast!).