Am I the first one to say "Guarneri" on this board? They've just been around so long and their interpretations are just excellent. That's in my opinion, anyways. Budapest Quartet was the best quartet, no doubts, but they're all dead and the recordings are old, so if one can't go beyond the surface noise... but I can, so I like them a lot too.

__________________
"Aufersteh'n, ja aufersteh'n
wirst du, mein Herz, in einem Nu!
Was du geschlagen
zu Gott wird es dich tragen!"
-Gustav Mahler

As others have said, it depends on the repertoire!

For Beethoven I prefer the Alban Berg's recent live recordings that were issued on EMI. Their performance of Op. 131 in C# minor is awesome. Same goes for the great A minor quartet too. I prefer them overall to the Takacs. For Mozart's 'Prussian' quartets I love the Alban Berg's late 1970s recordings on Teldec and for the 'Haydn' quartets it's got to be between the Chilingirians and the Mosaiques on period instruments. With Schubert it has to be the Lindsays (although I prefer the Amadeus Quartet for the great string quintet in C).

Now I'm aware that the Emerson Quartet has been mentioned... but I want to put in another vote for them, especially for their work on Bach's The Art of Fugue. Rich, I like the Alban Berg, too, especially their recording of the Debussy and Ravel quartets.

Nowadays, my choice is the Alban Berg, for any repertoire: the Viennese classics as well as the XXth century classics. I have had the opportunity to attend their concerts many times: and their live sound is powerful... I still recall an interpretation of the Lutoslawski quartet, it sounded like a symphony orchestra! The cello, Valentin Erben, may be in my opinion the best cello player I've ever heard to... Unfortunately some years ago, their former viola, Thomas Kakushka, died, and a young Isabel Charisius replaced for him: although she was Kakushka's disciple and plays Kakushka's own viola... well, it's not the same thing!

I also like the Takács a lot. They are splendid, their virtuosity has always left me out of breath... And the Borodin: their Shostakovich is always quite an experience, and their historic cellist, Valentin Berlinski, with his still magnificent sound, at 80 years...

The Tokyo have decayed a lot in the last years, they don't have anything to do with the splendid quartet they were once.

As for historic quartets, my favourites are the Amadeus and the Budapest.

Can the Janacek's quartets be played more beautifully??

Or Smetana and Debussy?

I attended a performance uf the Berlin Philharmonic String Quartet last fall and they were ther most humorless Teutonic stern-faced group I have ever seen. The contempt for the audience was quite evident and this was a performance at The California Institute of Technology which is one of the two most esteemed technical schools in the US. They are my least favorite string quartet. I know this is the opposite of the intention of this thread but I wanted to give my opinion of this group.

I go and listen to the Diotima String Quartet whenever I can. Their most recent concert that I heard was at Opéra Bastille where they played Beethoven's Op.132 and Nono's Fragmente-Stille, an Diotima. The quartet performs a lot contemporary music.

The violist of the quartet, Franck Chevalier, performed my Viola Concerto in 2001 with the Chamber Orchestra of the NZSO, and in 2002 the quartet participated in a recording (for Radio France) of my Tango Suite for contralto, string quartet & double bass. This was with Eiichi Chijiiwa and Nicolas Miribel as violinists.

The current members of the group are Naaman Sluchin & Yu-Peng Zhao (violins) Franck Chevalier (viola), & Pierre Morlet (cello).

Arditti Quartet, ABQ and Hagen (and Quartetto Italiano for old times' sake)