In terms of accurate color reproduction from a digital PJ neither Xenon nor UHP has any advantage over the other, not even infinitesimally so. This isn't a matter of "opinion". It has to do with the science of human vision. It isn't physically possible. UHP has advantages in that it is cheaper, brighter, and thus cooler for a given lumens output.
If you want some in depth explanation, you can do a search on my posts from a year or two ago on this subject. That will take you to threads where this was covered extensively.
To synopsise briefly and generally. The human eye has only three types of color sensors. One type each for the reds, greens, and blues. The amount that each of these sensors is stimulated by any given light source creates a "stimulation pattern" in the brain that is interpreted by the human brain as a color. The brain cannot "see" light spectra. It only "sees" stimulation patterns. Different combinations of light spectra can create exactly the same stimulation pattern. It is impossible for the brain to tell the difference based on light spectra. That is the essence of why even though Xenon and UHP light sources have differing native light spectra, they can create EXACTLY the same stimulation patterns in the eye and thus the same colors in the brain.
This fact of human vision is what our entire video system is based on. In Video there are only three colors: Red, Green, and Blue. The camera (or digital film scanner in the case of film based sources) reads only three colors: RGB. They are encoded into a video system which records only three colors: RGB. Ultimately, the encoded video signal is displayed on a display (PJ, DRT, plasma, etc) that only displays three colors:RGB.
In the case of a digital PJ, both UHP and Xenon lamps can be used to create the exact stimulation patterns that are the exact color of Red, Green, and Blue specified by the Video System.
Glenn