It depens, if nothing "important" is happening I play at X5 speed, and If it's something easy and feasable what I'm doing (which means I can trust the AI) and I am at war, I play at X4 or x5 (I.E Barbarossa after beaking the Soviets).
But if the war has started and it requires my attention I usually play at X3.
If I am roleplaying or doing other things while playing like watching the TV, or I want to think about something before acting, I can play even at x1 A LOT. And I must say that while having multiple theaters and roleplaying, I can really enjoy the x1 speed, because then I can just observe the AMAZING spectacle that hoi4 puts in front of my eyes, and all the statistics it displays and so on.
I've been doing achievement hunting for a while and while before it was unthinkable, now I find myself a lot of times playing x1 roleplaying and enjoying until everything becomes a steamroll and I just return back to the usual X5 . The problem? The AI can't compete with a human playing at x1, sometimes you just have to play fast and let the AI make some mistakes to enjoy the game with +1400 hours in it (and even more).