A lot really depends on the form factor; memory and RAID you require.
I use and recommend three i3770 processor based systems for ESXi that will not hang on "Initialising ACPI" when installing.
The shuttle has only one onboard non-Intel NIC, but has two available slots - so you could use these for an Intel AMT - it is a matter of finding the right non-esxi compliant nic. You could use the other slots for an Intel ESXi compliant NIC. The Shuttle to a good "transportable" ESXi lab which supports 32Gb Memory.....and with the special BIOS, does not hang.
The other two solutions are based in Intel Motherboards and both have dual nic's - one being supported by ESXi for use as the Management NIC (Intel 82574L) and the other not being officially supported (Intel 82579LM) because it provides Intel ® Active Management Technology (Intel® AMT) 8.0 support including KVM. I haven't tried, but you should be able to remotely KVM to the Intel 82579LM once you've configured this in the pre-BIOS interface and you should be able to remotely power up the PC's as well.
These motherboards are:
Intel DQ77MK - Supports up to 32Gb Memory; MicroATX Form Factor
Intel DQ77KB - Supports up to 16Gb Memory; ITX Form Factor
Although I have personally tested and used VMWare ESXi 5.1 for each of the above (and they are fine)........my "go-to" machine is the DQ77KB - mainly because I can put it in my backpack along with my notebook and take it into work each day. I have a 600Gb non-ssd configured as the datastore and I use a 128Gb mSATA drive on which i run Windows 8 as a "desktop" configuration. The system is configured to boot to ESXi 5.1 (with latest patches) and is installed on an 2Gb USB stick which is connected to one of the internal USB headers.
If size of computer is not an issue, the Intel DQ77MK is your best choice as it seems to want to have it "hard located" with the ability to remote to it. The shuttle and Intel DQ77KB are the optimal "transportable" ESXi Servers.
