I said flex, but I’m going to hedge a bit, because I like a more uptempo mindset to go with a 3-2, because you’re going to have more guard type players on the floor. You’re likely to have a speed advantage, may as well use it. Playing slow down can mute a speed advantage.
With a slowdown zone mindset, I would prefer a low post based triangle, with a 2-3 zone. Triangle de-emphasizes the conditioning attributes, particularly athleticism and speed. So in this setup, you have 3 bigs (ideally the forwards are excellent rebounders and defenders, and at least one of them can score, and the center is a rebound/block machine), and 2 guards, a distributor and a scorer.