Aprelflooring.com

There are few options to choose:

1) Floating floor. Engineered hardwood (with click or T&G glued) and Laminated (PERGO) floor. To be installed over sond-moisture insulating underlayment (foam). PROS: almost the only hardwood that is allowed in apartments/condos due to sound-proofing underlayment. CONS: the floor is not attached to the subfloor, feels "floating"

2) Solid or enginnered hardwood nailed to the wood subfloor. In this case a wood (plywood) subfloor should be built over concrete (two layers of plywood glued and screwed to each other, total thickness 1¹/4"~1³/4"). PROS: real solid nailed wood, unfinished or prefinished one. CONS: Contarctor should check if the floor can be raised for 2"~2¹/2" (subfloor + hardwood).

3) Engineered hardwood glued directly to the concrete. Often usen over radiant-heated floors. PROS:  can be installed on most house grades/levels due to moisture flexebility. CONS: cold if no heated floor underneath