There are a number of important factors that go into a successful online business. Hosting is one that is disregarded. Typically people think of web hosting as a utility (which it is) - but in the case of something like electricity there isn't much difference between one company or another. With hosting it's the opposite.
Many of us have struggled with crap hosts too many to name here. Downtime, sluggish speeds, and other issues are just some of the the reasons to have a good host. As we explain in Rank Hack Method - a fast host is even a ranking factor. That means getting a good host can increase your rank! We have proven this with client after client like Pre IPO Swap.
If you are using WordPress there is one host that stands out above the rest: WP Engine.
They aren't just a host they are much more. They will provide an entire experience with your site, meaning they will manage SSL, provide FTP, support, and much more. For a cost comparison it is going to be a little more pricey than the alternatives but you get what you pay for.
We use WP Engine for all our wordpress sites, so we aren't just promoting them without reason. We've been using them for years. They use AWS infrastructure so even if you are on AWS they have done all the wordpress config that probably you don't want to get into.