If your first floor is concrete, then I would go with the engineered. Nothing is stopping you from going to a solid in the upper floor over the wood substrate, unless for some odd reason, your second floor is pan poured concrete.

Solid wood and concrete don't mix very well.
Concrete has the ability to be below dew point at certain times of the year, or even certain times in a given day as a storm approaches.
Dew point is the forgotten element in solid wood over concrete. If the concrete is below dew point, so will the moisture barrier!