Further to Stewy's comments, the Omega has PS/2 ports as well as the printer port and can support rotating monitors (well, it will do...). The motherboard is a lot smaller (it will fit in our small 1U rack cases) and has flash ROM sockets going spare if you want to plug stuff in, plus the second processor(s) options when available. You also get speakers and a modem.
On the other hand, the Iyonix is available when you order one, is currently faster for most uses and can use bigger screen modes with more colours due to the video card. USB works and has plenty of things to plug in. It can take podules and is also usually cheaper.
Those are the main additional things I can think of. There's not a *best* one, there are two choices, one of which will suit your needs better than the other - it's pointless to then slag off the competition, it doesn't help the market.
Anyway, this is an Iyonix demo discussion - let's keep it that way, shall we?