Do I need a root canal or crown for dead tooth causing a terrible smell?

It sounds like you might have a gum disease issue or decay on your third molars. Hard to tell without xrays. You may want to have your dentist evaluate. Usually halitosis comes from gum disease, decay in tooth, or a systemic condition such as diabetes. Again, your dentist can help you.I would not be heroic with root canal and crowns for wisdom teeth.  Good luck.

The best solution to your problem is to have the third molars removed. It's really not worth the cost to do root canals and crowns on these teeth.