I didn't realize I had nostalgia for this game until I heard this.
As for objective best, I would have to say MNOG. It did such a good job of sitting back and letting the player explore Mata Nui, and made it a fun and engaging ride (unlike some games I know coughMNOGIIcough).
For personal favorites, I enjoyed MNOG, VNOG, Bionicle Heroes, and Glatorian Arena. Not saying they were necessarily great games, but I enjoyed them regardless.