Who wrote your favorite Romantic period SQ?

[Scion7]

Schubert is a classical composer, so no whining about his exclusion

Um, he is?  (Schubert's songs and symphonies are definitely in the Romantic movement, at the very least.)

[Scion7]

// And if you actually count Beethoven's late quartets as romantic (such as I do)

They are too abstract really to be called Romantic music - they are transitional works that skip the forthcoming Romantics and are almost Modern.  These brilliant pieces - which I would not argue if one considers them Beethoven's best works - stir the brain rather than the 'soul' like, say, the 6th or 9th do.

[Drasko]

Faure, or if he doesn't count then Schumann's first.

[mszczuj]

Dvorak

[kishnevi]

Don't actually have a favorite Romantic SQ.   I tend to go for Beethoven and earlier, or 20th century.  True favorite would be Mendelssohn's Octet (the String Double Quartet!)

If Beethoven counts as Romantic, it would be him. 
Otherwise,  a toss up.

So the best solution is for me to vote for

BRUCKNER.

ETA
Come to think of it,  I would go for Janacek if he counts as (Late) Romantic.

[yeongil]

Why is Smetana not on the list!?!?   Love both of his quartets.  I would consider Smetana my favorite of the romantic period (if we are not to count Beethoven or Schubert), but just barely.    Brahms (all three) and Dvorak (the last four or five) would be a very close 2nd and 3rd, respectively.