The important changes between the N55 and S55 are the S55's closed deck block, stronger pistons, sodium filled exhaust valves, double-piston high pressure fuel pump, twin-turbo system compared to single turbo system, and revised intercooling system. As stated as the start of the video, the S55 uses 75% of the same parts as the N55, so they're very very similar.

The S55 basically just has a handful of modifications which allow it to reliably produce more power and be prepped for track use. As far as which one is better, I think it's pretty obvious what the answer to that question is. The S55 is just an upgraded N55, there's really no downsides to it.

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