I believe that the answer(s) to your question are all going to be subjective to each person that responds.
You will have those that respond indicating that a small web host has less than 10,000 customers, while a large one has 10,001+ customers.
Same goes for servers or staff. Alternatively, you could look at how valuable the company is, if it's a publicly traded company, you could look at the market cap and see how large the company is.
For me, I believe that there is no fine line distinction between small and big web hosting companies. I would give an estimate that small companies are somewhere between 0-500 customers, 501-1000 customers for medium, and large being 1001+ customers. Web hosting companies come and go all the time because of how cutthroat the competition is. Additionally, there are a significant number of companies that aren't actual companies and aren't registered to do business. That's another thing to think about.
New webmasters practically all the time go with the most popular web hosting corporations instead of working to the small startup web host. Just like in the actual world, a customer is more probable to purchase a brand name product than to go with an anonymous brand. It is the same way in the web hosting world. There are numerous reasons for this:
A minor number of big and popular hosts hold the market share.
Big hosts have more money to expend on advertising and to develop their brand.
Big hosting corporations are seen as more dependable and trustworthy.
Though, after going through one or two big hosts you will shortly realize that just as its a bigger web hosting company, doesn't certainly mean they deal a improved hosting service.
While the bigger host can deal more resources for a much lesser price, the small web host is typically more willing to go out of the way to help you. It is hard to say which is improved because it really depends on your needs and experience. If you have a bunch of websites and know the ins and outs of website development, than you will likely find a large web host suitable. Though, if you are new and need guidance, than the small host is possibly the best choice for you. It’s worth the extra money to make sure your new website is impeccable.
Big hosting company have customer care team. They can solve your all queries within few second and small hosting company have limited clients that's why they don't have customer care team. They response each query within 24 hours.
Large companies have many experience as compared to small companies.