My first two votes go to a couple of the most popular,
Also Sprach Zarathustra, and
Eine Alpensinfonie. Then my love of the concertante form guides my next two votes, the
Oboe Concerto, and
Don Quixote with it's featured cello and viola. Finally my "other" vote is for the
Symphony for Wind Instruments. It may not be the type of work that Strauss is known for, but I find it very appealing. I'm always drawn to the sonorities of wind instruments, especially in ensemble, like Mozart's "Gran Partita" and Dvorak's "Wind Serenade". Thank you, larold, for bring my attention to this wonderful work and the composer's other works for wind ensemble.
His least well-known ouevre is his works that mimic his hero Mozart. Among others he wrote a range of wind music on Mozart's model, almost all of which is wonderful, well written, and full of lasting tune-memories. People think they know Strauss because they saw Rosenkavalier and/or heard the Alpine Symphony in concert but he has -- like Brahms -- a private or introverted side. Those are his Mozartean compositions.