"Hemp" is more common when talking about clothing, construction materials and any other physical use focused of its fibres.
Cannabis is the more common term used by government in the UK and most of the English speaking world.
In the USA it seems to be a 50/50 mix of Marijuana and Cannabis by the government there. Some people believe Marijuana is a word invented by USA government, designed to be scary.
On the streets, nicknames are more common. Weed is the most common nickname for it in the UK. Other nicknames used around the world include dope, grass, bud, pot, hash, mary jane, etc.