My adult suspense/thriller WAS 3rd person, multiple characters. In revisions, I saw the error in my ways and cut back to two characters. Many Critique Partners recommended putting the main character in 1st (something I toyed with anyway). Now, yet another CP suggested putting my other POV character in 1st.
I have not seen many adult thrillers with alternating 1st POV characters (other than GONE GIRL). But I HAVE heard that lots of editors HATE the 1st/3rd combo.
What is your opinion?
My opinion should not matter here. I haven't read the book. You should do only what the story requires. Do you absolutely need the intimacy of first person in both points of view? Do you need distance in one POV and intimacy in the other? What the story needs is what drives the structure.
That said, I think it's extremely difficult to carry off two distinct points of view in first person in a novel. Yes, Gillian Flynn did it brilliantly in Gone Girl. Yes, that was the brilliant exception to a lot of very bad manuscripts I've seen over the years.
There's a lot to be said for straight forward third person omniscient in a suspense novel. I like close third person a lot because it gives the writer lots more flexibility with getting plot on the page.
But again, this is YOUR story, and you should do what the story needs. It's easy for critique partners to suggest changes and sometimes they can see things you didn't but for structural things like POV, absent a huge gaping problem, you should decide and stick to it. Be confident in your choices.