I tend to switch between "Ok" and "Okay". Okay is my preferred use of the word though. I'm not of huge fan of just "k".
It depends on the situation. I'll use ok in most instances, but I used to mainly use Okay. If it's a casual circumstance, okie will be used.
"Okay" when I'm helping somebody, cause trying to stay as professional as a 12 year old can be, and "k" when I'm just talking to people.
Just fyi, I use "k" if someone's telling me to do a simple command, and "ok" or "okie" for everything else, if u didn't know
sometimes if someones joking around w me I go "k", and if I'm serious or I'm helping someone out I use "kk" or "okay" does "righto" count because I use that all the time
I usually use a mix of everything, but I usually use 'Okay, 'Ok', and 'Okk' It basically matters on my mood.
When someone writes me an emotional 5 paragraph essay in MLA format explaining all their feelings, I'll usually respond with "k". Other than that, I stick with "Okay".