one big site or lots of niche sites?

Authority site is best for long term stability

It is better to build one large authority site in your situation.

That way you can really focus on unity of content as well as building up stuff like social media traffic and even an email list.

I think high authority sites are best.

I'd also say, It will be better to build just one site and then contribute in every niche. Cause this will help you focus on every niche in the same time it will be usefull in the long run.

I think high authority sites are best also but I would still add more egg to my basket.
You never know what the tomorrow brings

High authority, I did small sites for years and now I'm paying the price.

One big website is always going to crush the little ones. Why? Because of the concept of singular focus. Don't underestimate the importance of stable efforts put into one project. That one site will continue to improve. When you build bunches of websites, the quality always suffers.

I have one large site & 2 smaller sites all in the same niche, so I can have an advantage when ranking multiple pages for same keywords. Between 3 domains, ranking multiple pages from the same domain & ranking thumbnail images in Google text search, I have 5 separate rankings on the first page for my best traffic keyword, lol, similar for other same niche keywords.

My advice is build a main site (your best site), then build a couple more same niche smaller sites & target the same main keywords, on the smaller sites funnel traffic back to the main site.

For instance, my main site is 100% downloads for my traffic, I have a smaller site that's 100% video tutorials that I made for the same niche, I promote the main site on the videos (video intro. branding of main site).

My 3rd site is a smaller version of my main site (100% downloads), same exact niche with unique content, targeting very similar keyword phrases.

Always track the incoming search phrases for all 3 sites, then target the good/new keywords across all 3 sites (strength in numbers).

About my opinion lots of niche website is better then one big website. If you post your websites backlinks into different small niche website then the backlinks counts of your website will be increase but if you post in the different section of a big website then your reputation will be increase but your backlinks counts will not increase. For the seo technique number of quality backlinks is very important.

Trying to manage 100 separate sites is going to be a massive undertaking. You'll have to do link building for each individual site not to mention managing email lists. All that done 100 times versus one time with a larger authority site. If you still want several sites, try to split your 100 niches into categories (such as all health and beauty goes into one category, all marketing goes into another) and put all similar related niches into each one. You might end up with five medium sized sites. That would be easier to manage than 100.

i had 10 niche sites all combined into 1 authority site and for some reason it got slapped on 16th December last year. Google stated there was no update, but something happened and i suffered. All i did in terms of bakclinking was a few manual links to internal pages.

But anyway, my point is, spread the risk. Going for 1 big authority site maybe not the answer all the time.

No one knows what will happen with their sites in future. Having only a single site isn't a good idea especially if you can't build a really high authority site. If your main site is penalized, then you'll face a very serious financial trouble. Instead having multiple sites is a great idea.

Yes it is harder to maintain multiple sites, but that guarantees that your future is somehow safe. If a single site gets penalized or something else goes wrong with it, then the others will keep earning for you. Moreover, you will also have a link pool of your own and by wisely using that link pool, you can rank multiple pages with ease.

One idea would be to roll all of your similar niche sites into one site. Try to pick a common theme among the various sites you already have up or want to create and then combine those into one site. That will not only increase the volume of content you have on each site, through the merge, but reduce your work load.

nowadays, i will vouch for big sites

The way Google has been trending I'd suggest looking at developing authority sites with authority website profiles.

While doing this, as Yukon mentioned, it's good as well to set-up a few smaller niche (or micro niche) sites you control to help further establish your authority site.

Importantly, if you try managing over 100 domains it's a HUGE hassle (trust me, we tried 300 domains...didn't work so well! lost several thousands in domain renewal fees and content)

You are targetting a good amount of niches. It is good to have a high authority site. You have to work hard to get good results.