That’s a very loaded question. So much will depend on environment, conditions, sealers applied, etc. Generally speaking though you should expect a good 20 yrs out of pressure treated.
Composite is worth it in my opinion based on look desired and how long you would be in the home. If you are adding it to a mobile home then no, I would not recommend it. Is it going on a 1 million dollar home? Then yes. Does it fit your lifestyle, home, neighborhood?