If in doubt, follow the POH instructions. For example:
BEFORE LANDING
- Seats, Belts, Harnesses -- ADJUST and LOCK.
- Mixture -- RICH.
- Carburetor Heat -- ON (apply full heat before closing throttle).
BALKED LANDING
- Throttle -- FULL OPEN.
- Carburetor Heat -- COLD.
- Wing Flaps -- RETRACT to 20.
- Airspeed -- 55 KIAS.
- Wing Flaps -- RETRACT (slowly).
AFTER LANDING
- Wing Flaps -- UP.
- Carburetor Heat -- COLD.
That's very clear: carb heat on for landing, and off only after landing or when going around.
FWIW, I was originally taught (in a C152) to turn carb heat on when throttling back on downwind, and turn it off again on short final in case of a go-around. However, no other instructor I've flown with does that and I now follow the POH procedure.
Since your instructors seem to differ on this it might be a good idea to find out what your local examiner prefers before you take your final checkride. That way you can be sure to do what he expects and avoid a debate about carb heat or worse, fail the checkride.