I had jk mapped for a long time and thought it was safe. Then one day I actually had to type it as text, and it took me a moment to figure out what was wrong. I'm retraining myself to use ^[ now.
I don't think the speed hit you take when you actually have to type 'jk' should be a dealbreaker. It rarely comes up, and when it does, you can use e.g. '<C-v>j<C-v>k' or 'jjkak'.
