By my own experience and via running authorities
@Barefoot Ken Bob (Barefoot Running Step By Step, Section II, Ch. 3. and position 1442 on the Kindle Cloud Reader) and Nicholas Romanov ( See The Running Revolution or the LearnToRun youtube channel), the clear answer that I deem as indiputable is the
ball of the foot, specifically the pad on the front of the foot that precedes the outside toes or the two little toes. The foot will then naturally roll on to the rest of the forefoot immediately thereafter.
Don't overthink or over-exaggerate this movement. If you run barefoot, it will be natural.
After that this is some debate about what comes next. I have always been a toes next and as little heel as possible, but after reading
@Barefoot Ken Bob last night, I think I may reconsider what comes next. I was reading the referenced chapter from his book just last night and was very interested in the fact that the ball of the foot is always first, but there is some flexibility in what comes next. But that isn't really your question.
What I do take as absolute wrongs are heel-first landings, toe first landings, and mid-foot/flat-foot landings. The first is somewhat a given in our running universe. The toe-first is how I first tried to front strike and my calves and knees paid a price. I have never tried a mid-foot although I had it recommended by some before I did my research. But the suction cup effect mention in Ken Bob's book seems clear enough for me to not go down that path.