so if i were saying i was something somethings tall.....wich would be better....meters...centimeters...or millimerter...

I really doesn't matter, but say if it were a building, then meters. Distance to the tip of Africa from where you are, then kilometers.
For the length of a pencil either millimeters or centimeters.
And so on...

When it comes to measuring height or length, the choice of unit depends on the context and the size of the object or distance you are measuring. Here are some guidelines to help you decide which unit to use:

1. Meters (m): Meters are commonly used for measuring larger objects such as buildings, rooms, or distances between cities. For example, if you want to measure the height of a tree or the length of a football field, meters would be more appropriate.

2. Centimeters (cm): Centimeters are ideal for measuring shorter distances or smaller objects. They are often used for everyday measurements such as the length of a pencil, the width of a book, or the height of a person. If you are measuring something that is less than a meter but more than a few centimeters, centimeters would be a good choice.

3. Millimeters (mm): Millimeters are the smallest unit in the metric system and are commonly used for very precise measurements. They are useful when measuring tiny objects or very small changes, such as the thickness of a sheet of paper or the diameter of a needle.

Remember, it is important to match the unit of measurement to the size of the object or distance you are measuring. This ensures that the measurement is appropriate and allows for easy comparison or comprehension of the given dimensions.