Prilipinï¿½??s Table. If the exercise is important enough that it warrants volume calculation (Push-Jerk, Power Clean, Deadlift) then you can figure out your optimal set/rep scheme with Prilipin’s table.
What about programs with set/rep schemes that aren’t anywhere near what Prilipin’s table calls for? Then just do what the program calls for. If it’s a good program, the exercise volume is already fine.
For moderately important exercises (Rows, Dumbbell Bench Press) I do 1-2 working sets and try to hit a PR for at least 1 of those sets. If I hit a PR in the first set, the second working set is heavier for less reps or lighter for more reps and more pump.
For isolation exercises (Rear Delts, Curls) I just make sure I do the exercise. I don’t write down the weight used. I’ve already been in the gym working out hard for an hour so I just let myself go by feel. The logic behind this is, if I’m going for PRs on Barbell Curls then I probably didn’t give enough attention to the important exercises.