Depends on what toys you like. ShadowRun 5th edition has been pretty good about not giving too much raw power in expansion books, more like options that let you focus differently than the main rules (possibly optimizing a bit more).
Overall I'd probably say Run Faster, for the qualities. Data Trails for the program carriers, commlink dongles, and the Smoke And Mirrors program. Chrome Flesh for some options on 'ware that are pretty good. Run And Gun for expensive suits that can give a small boost to your social skills and some of the called shot options. Fifth .... I'm not sure, probably Street Grimoire for the magical traditions, since some have some options that can be advantageous, and some spells that can be nice.