You would know the answer to this question if you knew anything about sales or copywriting.
You will NEVER see a copywriter asking "what product I should promote" because they know what a converting sales page looks like.
And then there is a small % of people who are naturally very smart, socially intelligent, and common sense alone will them which products to pick.
So for the mere fact you have to ask this question, that tells me you don't know much of anything about copywriting. And 90% of newbies I personally speak to, this is the 2nd biggest problem they all suffer from (the 1st being laziness). Because it's EASY to learn how to find good keywords. It's even EASY to rank a video or web page because once you learn keyword research... ranking is a no brainer.
But the most consistent and persistent problem I see is newbies can NOT sell. They don't know a thing about sales. They couldn't sell water during a decade long drought.
I suggest you create a list of some of the best copywriters who exist. Find all their best sales pages and put them together into 1 swipe file. Study their work relentlessly, learn why they do what they do, why it works, etc etc. Master as much as you can about copywriting. Because I can tell you for a fact, most the guys who are making 7 & 8 figures a year, they know copywriting.
If you have any other vague and ambiguous questions, please use the search button. Any question that pops into your mind, it's more than likely been answered 100 times already on this forum. And if you learn how to research, apply, research, apply, over and over and over and never give up, you can't fail. It's just a matter of what you're willing to sacrifice and how badly you want it. The guys who want it bad. They don't even bother making threads like these. They go register accounts, make a video, make a site, they DO SOMETHING and get to work IMMEDIATELY.