I'm sure Neji is fast enough to hit Suigetsu before he liquefies, so I give him the absolute victory in scenario 1
Scenario 2 is more complicated, Suigetsu is literally in his element so he's way advantaged and he would for sure manage to trap Neji in the water, all depends if the Hyuga genius is able to go through water like he did against Kisame clone. Anyway I see Sugi win more times than not here.
They're my number 1 and number 2 favorite characters lol