Whilst Strangeways Here We Come is my favourite album of all time, The Queen Is Dead is where I think everything came together for The Smiths, and it rightly deserves to be classed as their 'classic album'. The reason being, is that every single song has a different style and it showcases just what a talented group of musicians they were, and in Morrissey's case, what a great lyricist he was in being able to write with both humour and heartbreaking pathos.
As an initial fan I used to skip 'Vicar in a Tutu' and 'Some Girls are Bigger Than Others', why? Because at the tender age of 16, I found them embarrassing. Now I couldn't live without those songs, and I think the fact that Morrissey's lyrics can make people laugh, cry, cringe and gasp is what makes him utterly amazing. The tune to 'Some Girls' is also one of the best Marr wrote; such beautiful music and such daft, deft lyricism make it one of the best songs on that album.
However, I'd be hard pressed to say objectively which is THE best Smiths album, as The Smiths has a sense of urgency that can only be acheived by a genre defining debut, Meat Is Murder is difficult for a first time listener, much darker musically than their other work, but is such a rewarding album once listened to repeatedly, and contains some of Morrissey's best lyrics, and Strangeways is simply an 'album' in the truest sense of the word, from start to finish I've never skipped a track.
Overall though, if you were to choose an album to define an era, in terms of it's artwork, it's publicity (I'm thinking of the Salford Lads Club shot), it's songs / singles, and the statement it made, then I think The Queen Is Dead says it all. The Smiths are right there in the title alone, representing quintessential englishness, a great 'up yours' to the establishment, the freedom of the individual, intelligence, and a fabulous sense of humour.