Best to me means the company's history dealing with Medium Format, menu ui, sensor size, megapixels, lenses, price, stability of the company, and software support.
1. Fujifilm - A great system to get into if a smaller sensor and leaf shutter lenses do not concern you. Best value 100mp can be had for $3500-$4500
2. Phaseone - Best sensor size and megapixels. Other than that this company is far behind other camera systems with ibis and mirrorless how long can they get away with this?
3. Hasselblad - Best color, menu ui, native mirrorless medium format lenses until leica maybe? I know color is subjective, but I still choose this camera with the best color.
4. Leica - Once Leica creates the S4, I think it will become number 1 on my list because it ticks all of my boxes if they don't blunder their lenses like last time.
5. Pentax - This company is dead