That statement would probably go to Duna, because its a good starting planet. On topic: I would probably have to say Vall, I don't know why, but I think it looks cool and its not very hard to land on.
Career mode will bring a budget, meaning that you can't build as many ships as you want. Reentry heat will be added. Radiation is not in KSP and will probably never be implemented. If this was real life, chances are the Kerbals will have never even left the Kerbin System.
The Kraken is dead, it was related to bad physics calculations at high speeds. This is a new bug, so we need to come up with a name for it. How about the "Space Serpent?"