The greens have a 90 day warranty and are considerably slower. The blue & black are both faster but the blue has a 2 year warranty where the black has a 5 year warranty. FWIW, I've been using WD exclusively for over 15 years and have yet to lose a bit of data.
I currently use a WD caviar green 2tb as my primary drive due to failed SSD and it isn't any noticeably slower than any other platter drive for normal use. Maybe only a tiny bit in load times in games. Check the benchmarks and you will see that the WD caviar green drives end up very close to caviar blue in read and write speeds.