Its not enterprise class. Go for HP. Get a nice Gen 8 machine and you will be laughing
Sorry, but would disagree with this.
Supermicro products are designed and built for enterprise environments and use enterprise componants. What they do not do is provide the support services for 2h/4h/NDB etc warranty replacements.
Dell have used Supermicro boards in their products in the past (rebadged). One off the top of my head is the Dell C6100 (initial build) used a Supermicro X7 board.
Having said that, if experience of building ESXi servers is low then a ready built solution (HP/Dell/IBM) would be an easier way to go.
For a whitebox, the Supermicro X9SCM-iiF is a great E3 board ofr ESXi with the iiF variant using chipsets for the NICs that are fully supported by ESXi (the original didn't).
I would suggest load testing some hardware before fully commiting. Disk IO and ram are usually sticking points for virtualisation.
RB