Of those, I've only played The Nether Scrolls once and Sands of Fate once.

I honestly do not remember a single thing about The Nether Scrolls, which is a less than glowing review.

Sands of Fate has its own unique settings in an extremely high powered magic world (like children shoot Fireballs for fun type of high magic). I remember getting increasingly annoyed throughout the series about "Gotcha" moments where you as the player are simply screwed due to not knowing something -- one example would be a puddle on the ground that melted your boots if you walked through it...but there was no way to predict that and it simply resulted in the player having to reload. As I recall the third module in particular is a massive, massive dungeon crawl which has varying appeal.

Overall, I wouldn't recommend you play Sands of Fate unless you really, really have a burning desire to and have no other modules you'd rather play first. Nether Scrolls is a lot shorter and simpler and wouldn't create problems playing, though, I don't remember anything being particularly bad.

Neither of those modules (and none of the ones you mentioned, period) are among the best of the NWN community. I'd suggest you play other modules first -- a very short list of some modules I remember well is here as a starting point. Links are broken but you can see the summaries. There's also like half a dozen others I want to play when I find the time, also building stuff my own.

In particular, if you want a "consistent" story going from level one to high level the I would strongly recommend the Aielund Saga by Savant as it'll take you from 1 to 36ish. However, I am doing a few minor improvements on the series (with Savant's permission/blessing) which should be done in a month or two if you're patient. Fixing a few minor bugs most people never even find and cleaning up a few battle sequences (98%+ of the campaign won't be affected).