By far the best day-active octopus is O. cyanea, but they do get a bit large. There is a common, undescribed octopus in the horridus group from Indonesia that is day active and is much smaller, but they show up only occasionally. The mimic from Bali as well as wonderpus are also day-active - well actually wonderpus is crepuscular - but again they are hard to come by. Blue-rings are also day active, but I would advise against them.
Bottom line, for my money, if you can get a small O. cyanea from the Indo-Pacific, it will last in captivity for a year to 18 months (if you don't feed it too much) and you will have a great beast.
Gonodactylu