Choosing between VMWare ESX and ESXi [closed]

• The main difference is that ESXi comes without service console. I.e. it has a smaller footprint and therefore the attack surfaces is also smaller which is good if you don't like installing security patches (there are many security related updates for the packages that come with the Linux-based service console). The service console also makes it possible to execute scripts and install third party agents (for monitoring, backup, etc.).
• ESXi does not support VI Web Access.

Here's a nice VMware knowledge base article: VMware ESX and ESXi Comparison

Found this VMware ESX and ESXi 4.0 Comparison

The one from @knweiss was for version 3.5

ESX is also being depreciated. I believe ESX 4.1 is the last full version of ESX that will be released. All versions going forward will be ESXi-only. So if VMware's future is riding on ESXi, it's reasonable to assume so should yours.

Here's a blog post on ESX's sunset: http://blogs.vmware.com/vsphere/2010/07/esx-41-is-the-last-esx-what-do-i-do-now.html