How do you know that your story starts correctly?

Obviously, the most obvious answer would be: intuition or just pass it on to a friend lol. However, I refer more to the first and I would like a much broader explanation.

I have had a problem. And it seems to me a very big one, since my first chapter (or the first ones) seem completely crap to me. To summarize: in my story, people reincarnate in another world, just like that (they don't remember what happened in the last days before they reincarnated) and find themselves practically in a completely unknown place. From there come some start options:

1) Start at the Pre-rebirth (different setting, introduce the character and cliffhanger that urges the next chapter), and then move on to the next chapter Rebirth (discovering a whole new setting, continuous and interesting events). (Good way to provide context and background information about the main character and set the stage for the main events of the story. I think that this could be especially effective to create a sense of mystery or intrigue around the main character and the circumstances of his rebirth).

2) Start at the Reborn (interesting start, cliffhanger prompting next chapter, poor character introductions, discovering setting) and continue from there with flashbacks to introduce him. (It could be a good way to immediately grab the attention of readers and draw them into the story. It set a fast pace and create a sense of suspense right from the start (Or I want to think that).

3) Start at Post-Rebirth (start not so interesting, good character introduction, small cliffhanger that urges the next chapter a bit, clear setting) and then continue with the element of incitement. (It could be a good way to provide character development and depth and give readers a chance to get to know the main character before the story really takes off).

And yes, it is a fantasy and mystery novel. So I don't know whether to have a slow or fast pace, since most fantasy novels take their time to introduce everything (that's why I was guided more by Mistborn, since Vin's introduction is more progressive, but it seems that she really doesn't have a motivator at the beginning, which left me in doubt).

Aaand thanks to that, I've been left with an unresolved question for two whole weeks. I tried to go ahead with one of them, but I regret it and I say to myself "What if the other one is the best?", Since each one of them has its pros and cons of it.

How do you know what would be a good pacing and beginning in your novels?