I get a lot of questions regarding whether to use ESX or ESXi. I have been working with VMware for a long time and have loved using ESX because of the easy accessible service console. My recommendations so far have been:

New to VMware: Use ESXi – you have never used the service console and won’t miss it.

Already using VMware: Use ESX if you have special scripts and 3rd party applications that relies on the SC.

Last week I delivered my first vSphere Design Workshop. Some of the course content was very direct regarding this matter. Actually this is the first place I have seen it in writing from VMware.

§First choice is ESXi Embedded, whenever possible.
•ESXi is the future.
­VMware has announced its intention to eventually replace ESX with ESXi.
§Design the management infrastructure to support VMware® ESXi, even if deploying VMware ESX™.
•Limit the use of service console–based command-line management and monitoring agents.
•Develop ESXi management techniques now because ESX will eventually be phased out.