Best - 2006-07. Mick McCarthy inherited a depleted squad, expectations were low and through bargains, free agents and endeavour in spades, we made the playoffs. Jay Bothroyd scored some gems, Matt Murray was at his fricking best, and along the way, we beat the Albion! That's why in spite of whatever unpopular thing he's ever done, I still call him Super Mick.
Worst - 2011/12 - Just bad off the field as well as on. New signings disrupted the spirit of the dressing room, when Mick was sacked and Curbishley turned us down, Morgan had no Plan B to Z and stuck Clipboard Connor in charge. Demoralizing is an understatement.
I'd have thought relegation to L1 would have rankled a little more than the PL season!
Both the same; 08-09 was the most dire, turgid and depressing football for over half of it. Starting on-17 was bad enough but we were pretty much the worst team in the league anyway. A combination of Kevin Bond and then Jimmy Quinn managed to get us to 0 for Christmas, before we lost to the worst professional football team I have ever seen (Barnet) through our own ineptitude.
However, once Eddie Howe was appointed it became the best season; we hit promotion form and somehow survived with our last home game. The winner v Grimsby was a special moment and remains the biggest goal in our history (relegation would have led to liquidation, no doubt).
We've had 3 promotions since then, and last year was superb, with ludicrous football, winning a title and just shy of 100 goals scored; but nothing will ever top that finale in 2009.