Should ethernet cable be run in attic or basement floor joists?
It's common to run the cables in the easiest manner for your specific application. A lot of times, ethernet cable is run as a retrofit, and so the attic may be preferred slightly as it's more accessible. Given that you're running it in new construction, though, just run it in the easiest way you see fit. Your drops for cameras may go through the attic, as the camera itself may be positioned up high. Drops for jacks on the wall may best be run through the basement ceiling joists, or they may be best run through the attic. It all depends on the layout of your house and the layout of your runs. As long as you keep it away from the electrical, you're fine.

@AloysiusDefenestrate does make a good point to include a chase between all floors and the attic for future cabling. I'd go farther and say run conduit everywhere you can in addition to that chase. At the very least, include pull strings. Run 2 drops when you think you only need 1, and 4 when you think you only need 2. Run cables to potential TV spots. Cabling is super easy when the walls are open, and cable itself is very cheap. Go overboard now, even if a lot of it sits unterminated for a while, because you likely won't have this opportunity again.