The Twin Dilemma (Sixth Doctor).
I'm not sure I understand the strong amount of hatred this story gets or why the Sixth Doctor is generally reviled. The story itself was somewhat pedestrian but enjoyable enough. I also liked the Doctor's manic turns in personality although the groveling bit where he blamed Peri for their presence in the tunnels was somewhat exasperating.
Unfortunately I'm not going to get the chance to know the Sixth Doctor very well. The library doesn't have much of his material. Only The Twin Dilemma
, Vengeance on Varos
, and The Trial of a Time Lord.