A long time ago, sake was quite heavy in taste and less refined than the sake we know today – which was why people often warmed it up to enhance the flavor. Modern sake is made from polished rice to eliminate the unwanted flavors that come from the outer layer of the grain, the smaller the rice is polished, the finer the sake will be.
There are now many different categories of sake (classified depending on the degree of rice polishing, combined with other raw ingredients used) and most of them are suitable to drink chilled. However, there are sakes that are best enjoyed when warm, like Yamahai, Junmai, Kimoto and sometimes Junmai Daiginjou. I’d suggest trying the sake a bit cooler than room temperature first – to find out the bare character; from there, you can decide whether you want it warmer or cooler.
Usually, higher categories of sake like Junmai Daiginjou, Daiginjou, Junmai Ginjou or Ginjou are best drunk colder – but it really depends on the drinker’s preference.