There is no doubt in my mind about the worst sequel - Highlander 2: The Quickening. What an absolute dog of a movie! Not only was it crap in its own right, but in changing the back story established in Highlander, Russel Mulcahy and his team of hacks actually undermined what was an original and highly entertaining predecessor. Quite an achievement really.
For the best, I'd definitely include Aliens. James Cameron took a brilliant predecssor and turned it into something different and arguably as good.
Not sure whether The Two Towers and The Return of the King (the extended versions, not the theatrical releases) qualify as sequels, but if we get enough consensus that they are, I'll gladly add them to the poll for best sequels!
