Here in D5, 2-3 zone is the best way to go against most squads, because the players honestly shoot like high school freshman if you're at any respectable distance from the hoop. I've run a 2-3 in 11 of 13 league games, and I'm sitting at 12 and 1 and leading the league in scoring defense... and imho, it's a combination of several things that make that work best.
first and foremost, like someone already said, your PG and SG HAVE to know how to stop the outside shot, because against a lot of offenses you'll have those 2 guys covering 3 guys trying to hit outside shots.
2nd, your inside players need to have a good balance of the inside defense stats. by that I mean, shot blocking, rebounding, and of course general inside defense. those 3 stats are just above the bottom right corner of a player's skill table, should be easy to find. you've gotta keep those 3 running at peak efficiency and balance to make things work defensively.
lastly, one of the the best way to keep things running smoothly is to put together a squad that doesn't turn the ball over on the other end. you can help out any defense not let in baskets by making sure they have as few chances to do so as possible.
Now, as the shooting percentages go up, like in D4 and D3, I'm sure the 2-3 loses its effectiveness to some extent, because teams will have more outside shooting ability. but if you're in the lowest division in the USA, or just playing a team that likes to favor a look-inside offense, the 2-3 is the way to go.