When waterjet beats laser
Choose waterjet when material thickness exceeds laser capability, when the material is reflective or non-metallic, or when a heat-affected edge would compromise the part. Laser is usually faster and cheaper within its range, so the decision is mostly about material and thickness.
Tolerance and taper
Standard waterjet cutting produces a slight taper; dynamic head control reduces it. If your edge tolerance is tight, ask specifically what the shop holds on your material and thickness.