Satellite Laser Ranging (SLR) and Global Navigation Satellite System (GNSS) both measure the ellipsoidal heights. Which measurement of ellipsoidal height is more accurate?
In the ITRF2014, the vertical (height) components of coordinates are slightly better for GNSS than for SLR: ca. 5 or 6 mm vs. 8 mm WRMS averages, see Table 2 in Altamimi et al., ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions, 2016. (The full text is freely available at http://onlinelibrary.wiley.com/doi/10.1002/2016JB013098/full and was also reproduced in IERS Technical No. 38 "Analysis and results of ITRF2014", available for download at https://www.iers.org/TN38.) However, these are mean values for permanent stations and long measurements. A short measurement of a single GNSS station will be considerably worse.