This is the most important factor when choosing a web hosting service. Nothing else matters when your users simply cannot access your web site. A realiable web hosting service should provide at least 99% server uptime and 24/7 technical support.
If you need services related to email such as mailing list, webmail, auto respond / forward, etc, make sure you check with the web hosting service. Ask for any restrictions or limitations and ensure that it is suitable for your needs.
Disk Space / Data Transfer
Nowadays, more web hosting are fairly generous in terms of disk space and data transfer. If your web site is relatively new then this likely won’t be an issue for you. However, once you have your web site running on your web hosting, you should monitor your disk space and data transfer usage reguarly to ensure that you do not exceed the limits.
Web Language Support
If you plan to run any scripted web pages such as blog, e-commerce, or CMS, find out what your web language and database requirements are and ask if your web hosting service can provide such features in their hosting packages.
If you plan on creating an e-commerce web site or any web site that involves payment, then ensure your web hosting service provides Secure Socket Layer (SSL) support. This allows you to encrypt the data sent between you and your customer such as credit card numbers and other personally identifiable information. You may also want to check if the web hosting service provides any SSL Certificate services.
Your web hosting service location may have an impact on your web site’s user experience. A web page that takes a long time to load can be very frustrating to your users. Typically, it takes a longer time to load a web page that is hosted in a foreign country than a local one. If your target audience is from Hong Kong, then a Hong Kong based web hosting service would be more suitable. Similarly, if your target audience is from the United States, then you may want to consider an United States based web hosting service.