Which hardwood can you recommend? I have 2x8 joists on 16in centers. 1 layer of 1/4in plywood and 1 layer of 1/2in OSB plywood. under the plywood running between the joists is aluminum track with the pex tubing.

From what I've read so far, solid h/w is out.
Engineered is the way to go. Either stapled or floating, I'm leaning towards stapled.
Read a few posts here that discourage Braz Cherry over radiant, does that include the engineered as well? How about Santos Mahogany?
Any h/w or brands I should avoid. What has worked in this type of application?

BTW its the upper level of a split level ranch in upstate NY (Hudson Valley). Aprox 700sq ft

Stapled engineered is the way to go. It will feel much more solid than floating it.