Well, technically, a squid has two tentacles and eight arms. An octopus has only eight arms and no tentacles. The tentacles of the squid are relatively elastic and are the primary appendages (usually) used for hunting. They can be extended and retracted at amazing speeds.
There are some more differences between octopuses and squid that give squid something of an advantage. First, squid are typically equipped with hard, keratinous "rings" around their "suckers," and these are often serrated. When a squid grabs prey, these rings often dig in to the flesh of the prey to some extent, making escape difficult. This is why you often see semi-circular or circular marks on the bodies of beached or washed up sperm whales (inflicted, presumably, by giant or colossal squid). An octopus, on the other hand, has no such rings on its suckers. I'm unfamiliar with how powerful the suckers are between octopuses and squid, but I do know that octopuses can apply many, many pounds of suction per sucker disk.
Secondly, octopuses are known for short bursts of speed via a sort of natural "jet-propulsion" system, but aren't really considered "fast." Squid are very, very quick, and can maintain travel at relatively high speed thanks to the siphon/jet-propulsion system. It only takes a casual glance at a squid to realize that they're built to be speedy. A squid has an evasive ability and speed that the octopus can't hope to compete with.
The octopus probably has the advantage in terms of raw muscular strength. If it's able to anchor itself somehow to the sea floor and catch the squid, it's probably game-over for the squid, but the octopus would need to move almost uncharacteristically quickly. This is a far cry from the story we've probably all seen with the sharks in the aquarium.
Really, the two are so different that I can't make a call. In reality the octopus would probably try its damn best to avoid a fight, and the squid would probably just determine that the fight isn't worth the energy.