Setwise:

1. Slizer Engineering Master Race 2015 (best sets ever)
2. Old Slizer Engineering Master Race ruler 2004 (second best sets ever)
3. Babies Third year of Slizer Engineering 2001 (third best sets ever)
4. When Inika build tried and succeeded in being creative 2007
5. Return of the bright colours 2009 (visually a breath of fresh air after years of dark colours silver and grey, build wise was so so)
Honourable mention: 2016 (in terms of looks and enjoyment of the builds I would put it somewhere close to 2009, it tried but was not quite there visually, the Toa were visually downgrades from the 2015 ones)
Storywise:

1. Metropolis 2004 (future cities is love, future cities is life)
2. Battle for Giant Robot Bae 2008 (epic final showdown with all the most relevant cast of heroes)
3. MNOG 2001 (its the year of MNOG, need I say more)
4. Matoro Rip in peace 2007 (someone actually relevant died and stayed dead, water environment, serious business)
5. Takanuva, Mary Sue of Light 2003 (Conclusion of MNOGs protagonists arc from loser to Toa)
Honourable Mention: 2009 (It tried to do its own new thing and apart from 2015, it actually succeeded in it)