Is it uptime that determine the quality service? Is it customer support in multiple ways like phone, chat and ticket creation options which makes customer more comfortable with the hosting company in solving his issues? Is it 1 Click Installation feature for multiple platforms and frameworks like ecommerce, cms etc? Is it impacts to have the affordable purchase and renewal rates?
For me it's customer service. I've left a number of companies because I was less than satisfied with that. As far as the uptime, seems to me they all make close to the same promise whether they deliver or not. The actual experience would come in at #2.
Things to Consider Before Buying Web Hosting: Uptime Bandwidth and Network Location Processing Power Reputation
Google reviews about them/their domain, aks their support with various questions to see how they respond. After order, backup your data regularly so you can restore it with other provider if this one stop working.
Location differences can influence the speed of which a visitor gets to your website. Variables such as DNS locations can make a huge difference, if for example you have a small VPS or dedicated server based in Australia with DNS from the same machine, its likely load times would be significantly slower for visitors from US, UK etc to your website. If you use a Premium DNS service such as DNS made easy, cloudflare or have a decent host who provide multi-location nameservers then that takes that variable away and improves speed for users around the world. Requirements obviously depend on the site and the target audience of the site being hosted.