Are Jan Kubiš and Josef Gabčík heroes of Czecho　and Slovakia, or criminals?

The difference is that they were soldiers in the Free Czech Army, and their legitimate government was at war with Germany which had invaded and occupied their country. Therefore, their attack on Heydrich was a legitimate act of war.

Exactly as stated above, Reinhard Heydrich as the deputy Reichsprotektor conducted heavy restrictions and purges of inconvenient inhabitants of the Protektorat and also formed a conception according to which the Czech nation would be either enslaved or eradicated except for the few of appropriate racial signs willing to surrender who could be germanized. Apart from that, by performing the assassination, the Czech demonstrated that they refused to participate on what Germany was doing and that they were determined to fight it, despite having the opportunity taken away from them by Britain and France initially.

P.S. terrorism, in my opinion, is violence commited against civillians, not military officers (and authors of "final solutions" whose only wish is to obliterate half of the world and rule the rest).

Heroes.

Heydrich was the worst of all the Nazis - Hitler called him "the man with the iron heart" and the Czechs called him "Hangman Heydrich".Even Himmler was scared of Heydrich,so anybody who was directly involved in his death has nothing to be ashamed of.

As for Princip,talk to Serbs or go to Serbia to see if he's regarded as a hero or criminal there;it is the former...