If you are just embarking on a new installation of AX2012 you are best to install the latest CU so you start off the installation with the most current set of hotfixes. In this case you might want to create a slipstream install CD so that you can avoid two installs the hotfixes will be installed when do the initial install. This is a quick walk through creating a slipstream install CD with AX2012 R3 CU9.
While in this video I’m using R3 the concept is there in prior versions so you can follow the same if you are using a previous version and setting up a new test environment for example. The main difference in R3 is the access to the upgrade installer which is through Lifecycle services.