There are many variables between web hosts, but by playing it safe and choosing a reputable host you'll save a lot of effot and inconvenient website downtime - both at the live front end and in the private admin areas, and you can expect all the typical preferences to be included as standard. So to cut a long story short, the two major factors which determine the difference in value between the internet's top web hosts are Hard Disk Space (storage capacity) and Bandwidth Allowance (data transfer limit).
Stay away from claims of unlimited storage space or bandwidth allowance because it's an economical impossibility and many foolish webmasters have had their accounts terminated for 'abusing' (or simply 'using') such bogus infinute hosting offers.
Free web hosting is typically advertisement-funded. Depending on the host, these ads can be scripted into header and footer banners on every page, crashing some slower browsers (as with Tripod); or they could be solely on error pages, which often come with redirection to the free hosts' marketing pages (as with Atspace and Awardspace). Google Pages is probably the best free host, which limits its advertisement to the domain name (Google Pages websites are hosted only on googlepages.com subdomains).
For value and security, choose a large web hosting company. The best value web hosting is usually provided by large companies, because the scale of a large company permits "economies of scale" whereby bulk purchasing and general mass operation creates unrivalled efficiency. Furthermore, a large company is likely to have experienced and overcome more security threats than a small company, and thus the larger company will be more technically secure and will also have the capacity and resources to handle larger security threats than a smaller web hosting company could.
If you're a simple print graphics designer or general advertising consultant in need of a website, or any other non-techy professional, then you can be forgiven for sourcing a single agency to manage your website in its entirety. But if you can hold your own with computers and the web, maybe even as an aspiring webmaster, then you'll do well to split your suppliers.
Don't choose the same agency to register your domain name, design your website and host it for you too. Better is to divide such services between as many suppliers as is reasonably convenient.
If you've got a good domain name registrar you'll probably never have a problem with them. However, even the best web hosts have unexpected maintenance downtime, take sites down due to slander or intellectual property infingement allegations, or exceeded bandwidth limits (which may be caused by malicious flooders); change configuration settings and auto-update their software; and if you ever overwrite an important file and need a backup fast, or need to contact customer support for any other urgent reason, then you're going to want prompt support services with staff keen to develop a most favourable rapport.
The more dependent you are on your web host, the greater the risk of being unenthusiastically treated by their customer support staff. If you know you can easily login to your domain name registrars' websites at any time and point your domain names toward alternate web hosts then you'll be less dependent on any web host and you'll have more reason to be confident about expecting respect and enthusiasm from your hosts' customer service teams. But if your web host is the same all-in-one, total solutions company through which you've registered your domain names then you're rather awkwardly dependent on this company and you could find yourself struggling the swiftly resolve any complaintive issues which may arise.