My friend, this search is wrong: 'best niche ideas'
The correct search is: 'how do I find the best niche idea?'
If a niche is circulating in the market as performing very well, that niche is already dead. On YouTube, the important thing is being able to identify fresh, emerging topics. That means you'll either have to spend days and weeks manually researching and finding which videos have been viewed in a short time for which keywords, or you'll have to buy tools like trendtube, vidiq, tbuddy and similar services. If you really want to be original, this is the key. Searching for ideas online is just a hobby habit.