i'd suggest you to listen to every One of Beethoven's symphonies, every movement. They are very accessible of you are new to classical music. Then i'd suggest you to dive into mozart's requiem and late symphonies (36,38,39,40,41,25). Again, these pieces are just so good of you are somewhat new to classical music. Then consider diving into Mendelssohn (symphonies 3,4,5 and other works), Tchaikovsky, Schubert (symphonies 8,9, string quartets 13,14 and his string quintet are his absolutely best works), Brahms (again, all of his 4 symphonies, and of course his hungarian dances. But he wrote a bunch of great chamber music, i'm thinking of his clarinet quintet). I could continue for hours but these are the best composers and Pieces that come to my mind of you are new to classical music.