First person or third person?

I think it's really a preference thing. I have heard most people prefer third person unless it is a memoir type thing. Books do get published in first person.

From my own point do whatever best suits your story and does it the most justice for that story.
This is probably a question for Uncle Jim.

If you're telling the story in first person, you'll probably want to stick to that one person's narration throughout the book, which means that you can only tell about stuff that happens in the presence of the narrator. That works well with a mystery where the reader and the sleuth are supposed to have the same information available to them at the same time.

OTOH, it can be restricting, b/c if you want the reader to know something that happened off-stage, so to speak, without the sleuth observing it, you have to present it through dialogue, from someone who did observe it, and you may find that you'd rather show the thing happening, and you'd need another viewpoint character to be able to do that. Or, if you want the reader to be inside the head of a character other than the "I" narrator at various times in the book, you'll need a second viewpoint character.

There are examples of mixtures of first person scenes and third person scenes in a single book, or multiple first-person scenes, but it's complicated and hard to do well.

JD

Nearly all my novels are in first person. I was told (sometime after the 5th one came out) that 1st person was the most difficult POV to write--which was something of a surprise to me.

Yes, you are limited to that person's viewpoint, but if it's the best way to tell the story, then go with whatever is most comfortable for you.

If you need the main character in 1st, and supporting characters in third, that's do-able. Elizabeth Peters uses it in some of her Amelia Peabody novels.

In other books 3rd person worked best, and I stuck with that person's VP all the way through, so it's still similar to 1st person. Lois McMaster Bujold is brilliant at this.

In one book I had 6-8 different viewpoints to consider: 1st person for the MC, and 3rd for the rest. I just made sure to put in a break and had the name of the VP character in italics above the starting paragraph so the reader would know who was talking.