Thanks to @tbell for the card idea!
When I'm picking a team for basketball, I always want a fast player with good control (ball handling) to be my point guard. For me, Killua is the best choice. He gets to insane speeds with his Godspeed ability, and stays in control all the while.
You need to be able to rely on your shooting guard to knock down some deeper shots. The shooting guard needs accuracy, and Kazuto has some pretty accurate swordplay. He is always coming in clutch in his fights, so I'll say he is going to be that clutch shooter at the end of the game.
The small forward is your most complete player on the court. They can play around the perimeter as well as down on the block. They can shoot, block shots, grab rebounds, get steals, and dish assists. This is your most likely player to get that Triple-Double or that rare 5x5 (look it up if you don't know). Goku has speed and power, my main reason for picking him for this position.
Power forwards are especially good at grabbing rebounds and posting up inside the paint. You need to be powerful and need to have a decent jumping ability. The character that fits good to those standards for me is Tojo from Beelzebub.
A center protects the paint and needs to be able to block shots. They are usually tall and wide, giving them a big presence on the court. You don't want to see a 7 footer in front of you when your on your way to the basket. Alphonse in his armor is about 7 foot and, well, made out of metal. I'd say he makes a pretty good protector of the paint.