The objective worst case in the entire franchise is 3-1, since it objectively lies to you.
3-5 is probably the 2nd worst since it's the most contrived and pointless if you think about it. If Kibou didn't get hit by some stray rock, literally everything that happened in the game would have been for nothing.
Really each of V3's has some serious flaws.
1-3 is the worst trial in 1, but it gets too much flak.
2-3 is pretty bad too, but I'd have the worst trials of V3 over it.