For example, a good niche over the past few months would have been cryptocurrency affiliate programs as more people are starting to get involved with them but soon something else will be the new niche. Also, a good niche will appear but then other affiliates will figure that out then the niche becomes oversaturated and much more competitive
I personally think if you looking to make constant revenue through affiliate marketing stick to something you have a passion about or great knowledge in as your content will add more value. If you just jump from niche to niche you fall between the cracks and don’t get anywhere.