The mfgr info says staples or nails, so which is the preferred fastener? In this case I will be doing solid Brazilian cherry. I'm leaning toward nails. But if I were to do engineered wood later, would the nailer blow through the tongues?

Since my elbow has a new friend, Mr Arthur Itis, it will be a pneumatic nailer/stapler in either case.

Cleats are better and more versatile. They cost more than staples,though.

Ed:

If you do a search on the board quite a few lenghty discussions will show. Thinner engineered hardwoods will require different sized fasteners.