GRAMS
Neither of those units will produce a very convenient number. But of the two, the kilogram is the better choice.
Ounces.
Depending on the model and material; you can measure the mass using a suitable balance.
You would use the metric unit "liters" to measure the capacity of a hot water tank.
Metres
You would use kilograms (kg) to measure someone's mass in metric units.
You would typically use the metric unit of centimeters to measure the growth of your hair.
You would use liters (L) to measure the volume of a soda container in the metric system.
Depending on your location, it might be difficult to come up with a meter stick or a tape measure that displays centimeters and meters. It's probably better to measure it in feet and inches and convert it to metric mathematically.
You would use the metric unit "kilograms" to measure the weight of a bag of groceries.
Potatoes are sold by the kilogram.
A thermometer.