If I may add some of my own observations, I design and look at profile-cut parts all day long...
Waterjet: Comparably slow and expensive for metals. Tight tolerances can be achieved. +/- 0.005 is not unheard of, depending on who's running the machine and what they're cutting. Expect less than this from your average shop. Very thick material can be cut this way with very little kerf angle. Waterjet is amazingly fast on plastic, foam and food. No heat discolouration and a nice clean edge on stainless steel or aluminum.
Plasma: Not great for thin (say 14ga and less, give or take) if you want any sort of detail. That said, with some tweaking good results can be obtained with thin materials too. Inside corners will always be radiused, not square. Outside corners are usually rounded over as well because any sharp edge will just melt away as the arc passes by. Plasma is best, however for cutting outer profiles in say 0.250 to 3.000 steel depending on amperage. Hole diameter should be greater than the material thickness for acceptable results. Tolerances of +/- 1/32 can be held with good equipment and operators.
Laser: Very accurate, very temperamental. With tweaking I have seen hole diameters held within 0.003", but expect more like +/-0.010 or even 0.015 without special care applied. Because the beam width (kerf) is only about 0.012 to 0.015, that means the radius on inside corners is minimal and almost negligible. Most people overestimate the thickness capacity of CO2 lasers. Expect a good job done on steel up to about 0.500. Thicker, like maybe 0.750-1.000 if its a high powered machine thats having a good day, can be done but dont expect any sort of repeatability and the cut will look like a gerbil with carbide teeth gnawed it out of the plate. It will also be much slower on thick materials than plasma. Cut quality will usually look a bit ragged with vertical lines on the cut profile (a bit like that first picture in this post, but not as curved). It is not usually, as most people expect, a nice smooth finish. Materials less than 0.250 seem to have a better edge to them. Contrary to popular belief, a good commercial CNC plasma will often produce a smoother edge with less dross on thicker materials. Cost is reasonable, but higher than plasma or flame cutting. Thickness capacity of lasers is reduced for aluminum, and aluminum is often more trouble than its worth due to the materials ductility and reactivity. Many materials can be cut, but many job shops do not want to get special material in for a small job on a hobby budget (sorry, there is no nice way to say that).
Sorry to get a bit OT with this one. If anyone has specific questions on profile cutting that I have not already droned on about, Id be happy to answer in another thread or PM.
-Sparky
