How do I choose good fast growing privacy screen type trees or hedges?

Leyland Cypress grows very quickly and tolerates the hot, dry So Cal climate. Personally, I like Spartan Junipers better. They are a litle slower growing than the Leylands and survive longer. However, Spartans are harder to find. I don't know why because they are a great plant!

Here is a link to a Huntington Beach hometalker question which I answered a few months back which includes a beautiful picture of Lavenderstar Flower (Grewia occidentalis). Maybe this would work for you. https://www.hometalk.com/diy/grow/flowers/q-i-m-looking-for-climbing-vine-grewia-occidentallis-36193176?r=2

Poplar trees grow fast, and cedar.

Down here in Florida we are seeing and using a lot of a plant called clusia. It grows pretty fast and makes a fine hedge or fence.. If you are on zone 10 or 11 you could use it:

https://www.mygardenlife.com/plant-library/5198/clusia/species