I have owned both. I personally like the 32HD more (runs quite). However, for your application, I would go with 2 16HD. Look up brstv 16HD video, they set it up on a 40g breeder.
You could always use a 32HD and not place corals on the side. It would just not look great. The light drop off will be very visible. You can also start with one 32HD and add another one later, If needed.
2 16HDs - spread is huge, one of the things you don't notice that you notice it until it's noticed. Also 2 16HDs have more Watts available than 1 32 does so if down the road you add some more light demanding corals you'd have a little extra light available.