Saint-Saen composed 5 symphonies, but 2 were published posthumously, so the Symphony No. 3 is actually the last symphony he composed. Known as the ‘Organ’ symphony, it is the only one of the 5 symphonies that is really in the basic repertoire. However, there is quite a bit to like about the other 4, and worth a listen.
The best classic performance is by Charles Munch and the Boston SO on an RCA Living Stereo issue, with a wonderful performance of Debussy’s La Mer.
If you want to check out the other symphonies, Jean Martinon recorded the entire set and to be honest, I may like the ‘Organ’ performance a little better than the Munch. Either way, both are worth a listen. Performances of the ‘Organ’ by Ormandy is also good if you prefer, and includes ‘Carnival of the Animals’. The Martinon set is available used in several releases, and some are more of a bargain than others, just search for Saint-Saens Martinon.