I recently upgraded to HD for my DirecTV service, which included their new H20 STB. When connected to my HDMI compatable display, the picture appears to be slightly sharper than with component. However, the H20 STB seems to have problems (fewer than reported with the older H10 STB) - it exhibits signal (audio & video) drop-outs which are very distracting. Therefore, I'm using the component connections for reliable, quality, audio & video.
IMHO, HDMI (any flavor) only works when the source, cables, and destination (and any intevening boxes) are all fully compatable, and compliant, with the full HDMI specification (1.1, 1.2, or 1.3 as applicable). Not all manufacturers/signal suppliers have gotten their act together yet.