Plenty of cool robots being thrown around here, but for my money, there are a few indisputable answers that moved the ball forward on what we thought was possible or forced a significant change in the rules. Most of these have already been mentioned, but my takes:
47 in 1998. The lasting effects of Chief Delphi’s introduction of swerve drive to FRC can’t be overstated.
71 in 2002. You can’t use traction materials that damage the carpet anymore, and this edition of the Beast was also (I’d argue) the most significant bot that flopped in FRC history (although not the most significant for being a flop-bot, per se).
67 in 2004. There were others, but I think the 2004 HOTBOT was the most memorable among the series of machines that strategically expanded their footprint in the pre-mandatory-bumper era.
469 in 2010. Probably the last of the “game-breakers” and the only one to fall in FRC’s modern era. Las Guerrillas were the most refined among a small cadre of teams that skirted along the edge of Breakaway’s ball control rules to inventively dominate gameplay.
1717 in 2012. The D’Penguineers’ Lindsay Rose featured what was undoubtedly the most technically advanced swerve drive FRC had seen to that point, and it was driven with an equal level of finesse.
148 in 2015. The Robowranglers debuted arguably the most creative robot in a year that provided no shortage of them, with two specialized halves tethered together to multitask like no other team could.
Honorable Mentions—Near Misses
68 in 2003 and 118 in 2012. (With acknowledgement of some homerism for my own former team) Both these designs were struck down before they could take the field for similar “reacting against multiple sides of a field element” violations.