Rationality i'd pick Invincible season, in terms of achievement its bigger. Also it is a statement in terms of progress as it requires a consistently high level. CL is more prone to randomness.
Though there's arguments for the emotional highs that winning cups and finals bring.
Currently i'd say invincibles, ask me in May and I will probably say the CL.
Tough. Stating the obvious here but the UCL is the biggest hole in our trophy cabinet. But another invincibles title, on our 20th anniversary of the first one? I think you have to take that.
Invincible. It stands above all other achievements. And the anniversary. To go invincible in this day and age would be somehow even more insane than what's come before.