I think you have a few possibilities.  My first choice would be Octopus cyanea.  If you can get a small one, they will live for a couple of years.
Perhaps easier to come by and living just as long is O. rubescens.
The easiest to find is A. aculeatus, but rarely do they survive more than a few months.
By far the best choice would be a Larger Pacific Striped Octopus (not yet named).  Dramatic coloration and behavior, diurnal, iteroparous, live for a couple of years and tolerant of a wide range of temperature.  You can also keep a male and female together.
Roy