I've commented elsewhere about how having a pet is setting yourself up for grief. I understand the feelings towards dogs, cats and the like, but having to put down a loved pet every eight years is more than I care to deal with.
A few years back, I was taken with the idea of keeping either an octopus or a cuttlefish. Both are extremely intelligent and have personalities of their own, which is pretty extraordinary for animals that share more with snails than they do with mammals. (Octopuses (the true plural) can even escape from a poorly guarded tank, walk across the corridor to an adjacent fish tank, climb in to the fish tank, eat the fish, and then crawl back into their tank and sit there, staring out at anyone who dares to suspect them.)
Two things put me off of the idea. One is that you need a huge salt water aquarium to maintain them in good health and spirits. Salt water tanks are hard to maintain and very intolerant of any variation in water chemistry.
The other was the clincher, however. Both cuttlefish and octopuses have a lifespan measured in months rather than years. Having one as a companion for a short time would not be worth the grief in losing them.