Time for a quick drive by from me, too...
Easy to answer best season from my perspective, like Badge, it's got to be 1993 (my sophomore year, and I went to see the Rose Bowl live). Best team? Hard to argue with '93, but hat tips to '99--that was a beast of a team in a very strong Big Ten, 2010 and 2011--both really talented teams that were *this* close to true greatness, and 2017: all that and more, 13-1, Orange Bowl victors (going away from a good Miami squad). Oh, to have that conference championship game back...compare that six point loss to Ohio State to the seven point loss to a really bad Minnesota team in '93--which team was actually better? Pretty good argument for the 2017 version.
Most disappointing? There are a handful to choose from:
1995: 4-5-2 (that's right, two ties!), two years removed from the Rose Bowl win, and finished the season with the last tie in the history of college football, a 3-3 snoozer at home against Illinois over the Thanksgiving weekend. Wisely, I spent Thanksgiving with a friend's family near Milwaukee, and we made no effort to get back for that game.
2001: also two years removed from a Rose Bowl win, a team that nearly beat a really strong Chip Kelly Oregon team at Autzen (the Ducks finished the season #2, with a Fiesta Bowl win), and beat Ohio State (turns out they weren't so good), and nearly beat a good Michigan team, but got blown out by Indiana (I don't care if it was "good" Indiana--it was still Indiana), lost to Fresno State (!!!) and Illinois, and lost by two scores to Michigan State and Minnesota. Ouch. The other (with '95) sub-.500, post '93, Alvarez season.
2008: Bielema's biggest trainwreck. The team finished with a winning record, but had way too much talent to play as poorly as it did. (7-6, loss to FSU in the Champs Sports Bowl). That team had five offensive lineman who had meaningful NFL careers, some solid wide receivers, including Gilreath and Nick Toon, TE(-ish) Travis Beckum, as well as Garrett Graham and Lance Kendricks were all good, but oh, it was the defense: O'Brien Schofield and Matt Shaughnessy were beasts on the line, as were DeAndre Levy and Jonathan Casillas at linebacker, and in the backfield Chris Maragos, Jay Valai, Aaron Henry, and Allen Langford were all solid. And for all of that, the team was completely mediocre. Maybe they weren't world beaters, but they should have been a whole bunch better than they were.
Honorable heartbreak mention for Bielema's last team, 2012: went 8-5, 4-4 in conference, finishing third in the division. So pretty mediocre, right? Because Ohio State and Penn State were ineligible for post season play, Wisconsin played and destroyed Nebraska in the Big Ten championship game, earning the right to play in the Rose Bowl--under Alvarez because Bielema decided to try pork--where it lost to Stanford by one score (Stanford finished the season ranked #6). So pretty mediocre. But oh, how that team lost. By three at Oregon State. By three at Nebraska (but see the conference championship game rematch: UW 70, Nebraska 31). In OT to Michigan State. In OT to Ohio State. In OT at Penn State. And the Badgers spent most of the second half of the Rose Bowl down 17-14, until a late field goal made it 20-14. Still they had time, but an interception ended their hopes. It was just that kind of year.