Does it matter share host or cloud host?

Thanks for reply, Paul.

Actually I'm thinking if thousand(or much more) users be online on my web app and they do some actions(in a short period of time), what will happen?
That is very important to me.

I heard about 'Carousel.com' website(if you be familiar with that) that they were using DigitalOcean as a cloud hosting and they got some issue about multiple users action(Im not sure how much this news is true). another hand I'm hearing a lot about this issue on shared hosting.

About the compatibility of host with CI3:
i can see 90% of the hosting offers the plans for Wordpress, Ruby, python. but i couldn't see any anything about CI !