This is the largest quasar catalog published (to 2016), and has the most accurate astrometry with arcsecond-accurate positions for all objects (can be 2 arcsec for some legacy quasars).
This Half Million Quasars catalog (HMQ) includes data up to January 2015, including SDSS-DR12Q. 510764 total objects are included from the literature, including 424748 type 1 QSOs, 26623 type 1 AGN (like QSOs but extended, e.g., Seyferts), 25015 high-confidence (99%) photometric quasars from SDSS-based NBCKDE / XDQSO with radio/X-ray associations, 1595 BL Lac objects, and 32783 type 2 objects. Radio and/or X-ray identifications are shown where applicable.
The ReadMe is here. The preprint paper is here. Citation references list is here.
Download the file here in FITS format or as flat text. Quick browse of sample flat text data is here.
Publisher's page (DOI): 10.1017/pasa.2015.10 . ADS page: http://adsabs.harvard.edu/abs/2015PASA...32...10F .
The flat text file is also available from VizieR -- select the FTP tab and download files from there -- be sure to get the references list from there also.
The VCV Optical Catalog
HMQ uses the Véron-Cetty & Véron Quasar Catalog (VCV: 2010,A&A,518,10) as the authority for pre-2010 quasars; however, these needed to be converted to long names and their astrometry shifted to their true optical positions. In the process about 3% of the VCV objects were found to be stars or galaxies (mostly because of misclassifications by SDSS-DR7), or duplicates, or not to exist. The counts are: 168,941 objects presented in VCV, of which 157,464 are found to be type I (or BL Lac type), 4662 are found to be type II, and 6815 are found not to be quasars.
The optical mapping of the VCV catalog is available as 4 tables equating to the four original VCV tables (table1=QSOs, t2=BL Lac type, t3=AGN, t4=false objects), plus a ReadMe, all zipped up into a single file. Get it here
Eric Flesch, last page edit 26 January 2019