Floating or Flat designs are just part of a design language, these are small standards that you incorporate in your design. Is flat or floating better than the other... perhaps but have fun with that debate.
What to choose
What is more important is that you as a designer understand the value your UI designs bring to the User Experience.
I personally prefer floating UI as I adopted the design language by google "Material Design". However, that being said sometimes I find value in flat designs depending on my demographic and medium. As an example I do not use gradients (dropp shadows) for print design because gradients don't always translate well to ink, they can run and look like they have a banding effect.
If I am designing a product for windows based users then material design language is not quite as familiar in their day to day experience with software as windows uses Metro design which is utilize alot of flat designs.
Dig deep, understand the value that both design methods bring to the table and choose the one that helps you represent your information architecture to your users.