What is the best units to use in CSS

[Ricoool]

What, do you think ?, is the best units to use in CSS, if you want text to be able to change size according to whatever the user sets in the browser

Ex. 1
body { font-size: 1em }
p { font-size: 90% }

or ex. 2
body { font-size: 1em }
p { font-size: 0.9em }

[seonewbee]

To use "em" dont you first have to define the font size in the body?

So, it should be:
body { font-size: 12pt }
p { font-size: 90% }

or

body { font-size: 12pt }
p { font-size: 0.9em }

[Ricoool]

wont it just adapt the size of the borwser settings ??

[Ricoool]

Anyone know ?