OFF unless required.
You only need to use heat if you are in or likely to encounter icing conditions, which is <5'C and in/near visible moisture
Some of the previous arguments would suggest that they would rather fly with the Carb Heat on full time instead of having to remember to cycle it reguarly.
Pitot Heat is a anti/de-icing function. No need to have it on when not required. Not only are you protecting the elelment from premature failure but you are protecting the other parts of the electrical system which when it fails due to overloading, could really make your day.
S2K