40 degree for body paint. 25 might be okay for wheels and other tough parts but be careful to only hold it as close as needed to knock the dirt off.
25 degree on a 1.8 gpm / 2000 psi unit did a great job on our wood back steps, but at 3gpm and 3000 psi, you might start tearing off paint and eating into the wood. 15 degree strips paint and carves into wood, whereas a 0 degree jet tears holes through wood and asphalt.
General rule for cleaning is use the least aggressive action/chemical/tool that gets the job done, so start with wide nozzle and lower pressure settings and work your way up as needed.