Which type of hardwood floor is better with a concrete radiant heat floor - floating or glue down?

We are most interested in the effects of VOC's (volatile organic compounds) and if we do use glue down which is the best brand and specific type of that brand to use to glue down a hardwood floor on a radiant floor?

View this post on my blog: http://madeinhome.info/which-type-of-hardwood-floor-is-better-with-a-concrete-radiant-heat-floor-floating-or-glue-down