It’s the best place to find RP at any time of day, yeah. Random RP sorta stuff. You can also find a whole lot in the Royal Exchange district of Silvermoon.
If you want to get away from the casual stuff in the cities your best bet is to find an RP guild. Guilds organise RP events and whatnot outside of the normal hubs, but might not be active all day every day. For example my guild, Lordaeron Unbound, do a lot of our RP in the Eastern Kingdoms, based around Fenris Isle. But it’d be tricky to just find us in a walk up RP because we’re not ALWAYS there, you know?
So basically if you want casual RP anytime in the day to meet strangers and build connections, Orgrimmar or Silvermoon are the places to go!
If you want more story-driven and preorganised stuff, a guild is the best way to go. You can find a list of currently active RP guilds, on both factions, in this thread: WrA Information & Directories (Guilds | Communities | Events)
Personally I recommend a bit of both. If you meet people in random RP in Orgrimmar you can build connections and make friends. That’s how I met both my IC guild officers, actually! However it’s also nice to get out of the cities so an RP guild can be a really cool thing to check out.