The Royal Exchange and Murder Row of Silvermoon often have RPers around if you’re looking for Hordeside.
Otherwise you tend to see Alliance-types in Stormwind 
If you’re looking for RP outside those spaces though I 100% recommend giving this community a look. The intention is to make finding RP easier! So for example if you wanted Illidari RP in the Demon Hunter Spaceship, maybe you’d find it in here
https://us.forums.blizzard.com/en/wow/t/ah-lfrp-community/696658