What is the maximum size of parts you want to make? What are the materials you want to use?
I have an MV3 and a Fireball V90. I'd recommend the MV3 in an instant if you want to mill light materials and your projects fit within its "A4" envelope. It is strong, stable, and you'll be up and running within 2-3 hours of receiving your parts.
I also know someone who has a Romaxx HS-1. He swears by it. It machines around the same size as the V90, but I think you'll find it is much more strongly built. If money was no object I'd choose the HS-1 over the V90.
I have no experience of the K2 machine.
I wouldn't touch one of those Chinese machines with a ten foot pole. I'd also be very careful of buying an eBay machine, unless it was a combination of supplier and machine that has a good reputation in CNCZone.