Keeping the discussion about physical-virtual apart from this comment:
1) Microserver N54L & older N36/N40L (the black and cheapest ones):
- very good for Sme stand alone, tried with 7-8-9, ahci supported for 8-9;
- the only chance to use it as Hypervisor is Proxmox, not the native CD but in this way:
https://pve.proxmox.com/wiki/Install_Proxmox_VE_on_Debian_Wheezy (to have software Raid);
2) Microserver Gen8 (Grey and silver, more expensive but not so more):
- very good for Sme stand alone, tried 8-9, ahci mode supported;
- Hypervisor with Vmware Esxi 5.5u1: possible with native Raid with B120i integrated controller (it's an Intel chipset less fake than its predecessor) supported with the Hp-customized Vmware CD;
- Hypervisor with Proxmox: you can surely install in the way suggested above (1); never tried with native B120i Raid;
In both situations for entry-level hypervisors, Raid 1 is suggested for decent performances in a production environment.
For your personal experience Esxi gives you experience on a more popular product with large support, knowledge and applications (free and not) and support for veteran OSs (sometimes very important).
Anymore Proxmox is very good too: I presently use for my lab and for a few weeks has worked fine with a SME+Affa vm to replace a failed server.
Nicola