Here a few words about the lab setup I am using.
– Notebook HP EliteBook 2560p Intel Core i7-2620M 2x 2,7GHz
– 16 GB RAM
– 500 GB SSD
– Notebook running Windows 7
– VMWare Workstation 12
ESXi is installed inside of VMWare Workstation 12 (nested virtualiziation). Works perfect and has lots of advantages, like you can make snapshots of the ESXi installation, clone the installation (with all the VMs inside that installation) and so on.
Inside of VMWare Workstation also the two client machines for development are installed, one Windows 7 and one Ubuntu 10 machine.
Note: Seems like it is not possible to use nested virtualiziation with Oracle Virtualbox.