My preference is 1. waterjet 2. hydefinition plasma.
Cost wise: Waterjet's are very steep - 130k (used) to 300k (used) or around 220-600k for new. Oxygen plasma cnc system - 20-30k. Hydefinition plasma cnc system 60-250k.
Waterjet cost the most to operate. It cuts 10x slower then plasma. Parts are ready to ship right off the table. I regularly cut parts that hold +/- .001 tolerance. I can cut any material I put down on the table. I regularly stack sheets, so for instance copper gaskets, I cut 5 sheets stacked at a time. The resultant speed is faster then plasma or laser when you factor in you are cutting 5 parts at once. Waterjet's come with a significant cost of operation and maintenance, and it's not uncommon to have one go down for a week or more if you have trouble determining the issue which happens. We were down once for a month and a half. This year alone I've spent $30k on waterjet maintenance & consumables. However, we also run them 12 hours a day.
Hydefinition plasma cut looks very similiar to laser. It has a wider kerf then waterjet (0.080-.120 versus 0.030), has more spatter, but it has minimal taper compared to the oxygen plasma and it's very fast. With a good xyz system you can hold .005"-.010" pretty commonly with good consumables. The cut quality and accuracy are all related to the condition of the consumable, and where oxygen plasma just uses compressed air, hydef's use as many as 5 gases to get a good cut and maximize the consumable life. This doesn't come for free though, the consumables and high gas usage is a significant cost. You can retro a hydef power source to a standard xyz table pretty easily, but torch height control has to be addressed at the same time. It needs to be accurate to .01 V.
Oxygen plasma cnc systems are everywhere. Those are the torchmates, plasmacams, etc. They run hypertherm, thermal dynamics, etc oxygen power sources. They will give you an ok cut. If you are ok with spending a significant amount of time cleaning up parts, want to spend under $30k, and want to limit your spending to just torch consumables and not industrial gases - then it might be a good match. I haven't dealt with these much, but I have customers that send us plasma flanges for their assemblies, and they always look and weld like crap.