Most supermarkets only carry the standard sized purple-and-white arms at the top, but if you shop at a more upscale place like Precce in Midtown, you can choose from a variety of cephalopod species and sizes. I guess there are some people who especially like the big suction cups, while others will take their suckers small, thanks.
Confession: though I never bought an octopus, I did once buy a squid, much like the one staring out at you from the picture. It was circa the autumn of 2003, I believe, and having just seen a Japanese cooking show on how to gut and slice them, I wanted to give it a try. I won't go into the gory details, but there was black ink involved and a horrendous stench in my drain for days afterward. Now just looking at this picture gives me the creeps. Uugghh... !