Brahms' fourth is a favorite here too, a marvelous synthesis of the whole romantic, classical and late baroque period. If anything, I think that Brahms was certainly one of the most perfect composer there ever was, the consistency of the output that he's left us is just mindbogling, unlike most others, he doesn't really have such things as immature works. The fact that he destroyed every single of his compositions that weren't up to his absurdly high standards probably has something to do with this, but that still leaves us to a little over 100 opuses, which isn't small by late romantic standards.
But anyway, the symphony of his that I like the most is the third, with its earthshattering finale (which gets me like nothing else), its hearth wrenching third movement, and the stupendous first and second movement, in all their elegance and chamber-music like restrain (though they both have sections that are quite symphonic in character, the process of making them fit this perfectly together must have been awfully complex).
I like the first too, but it's not as Brahmsian as the others, there's a bit too much Beethoven in it I think. In my mind, the two aren't as similar as some people make them to be, there's a restrain, a calm and an almost Schubertian wandering spirit in Brahms that you don't find in Beethoven, whose music is clearly more assertive, ambitious and in some cases, more unabashedly intellectual than anything the other ever wrote.
And as far as my favorite recordings of those symphonies, Furtwängler/Kleiber for the fourth, Klemperer for the third (doesn't completely fit with my own view of the work, but it's a great performance nonetheless, I still need to listen to Furtwängler here too) and Furtwängler again for the first.
And on the refreshing classical music front, Mendelssohn's (HERESY!) chamber music has had its ways with me lately. His sixth quartet is something to behold, the octet is a masterpiece, and the first piano trio has its moments of pure bliss.