Where I live, 10 months of the year it makes no difference because it's going to be rock-hard and able to bend your knife no matter where you keep it. The remaining two months of the year butter left on the counter is a glorious yellow puddle.
Butter stays hard below 15 C (depending on variable like fat content). Fridge is 4 C. 8 months of the year my kitchen is below 15 C. I do not live in the tropics or even the subtropics.
