S-500 Prometey is the latest, but are not operational yet. So the S-400 Triumfs, aka SA-21 Growler, are the latest. How effective the particular S-400 system is depends on which fire-control system is coupled with it.
The S-500 will significantly out class the S-400 with 6th gen radio comm and many other features.
See this Tyler Rogoway article on the S400 system (Tyler has since left the site he founded for a job at Time and the site has gone downhill since).
http://foxtrotalpha.jalopnik.com/heres-russias-s-400-missile-system-in-action-and-heres-1746490022
Thanks! Good ref I did not know about. :D