George Edward Pickett
No single group of men at West Point has been so indelibly written into history as the class of 1846. The class of '46 fought in three wars and produced twenty generals total, ten on the Union side, including George B. McClellan, who survived the war, and nine on the Confederate, including Thomas 'Stonewall' Jackson and Ambrose Powell Hill, both of whom were killed, and George Edward Pickett, who had graduated last in the class.
The number one man in the class never made it higher than colonel during the conflict. McClellan had ranked second. Jackson, who had no formal education until he entered West Point at the age of 18, graduated 17th in the class. Originally a member of the class of '46, Hill's graduation was delayed one year when he contracted gonorrhea in the summer of 1844. He graduated 15th in a class of 38 in 1847.
http://www.civilwarhome.com/pickettbio.htm
A few other class rankings of interest:
Robert E. Lee graduated number two in the class of 1829.
Union General George Gordon Meade graduated in 1835, ranked 19th of 56.
Confederate General James Longstreet graduated in 1842, ranked 54th out of 56.
Ulysses S. Grant graduated 21st in a class of 39 in 1843.
http://thomaslegion.net/unitedstatesmilitaryacademy.html
Asked to name the best Union general, Lee answered George B. McClellan, commander of the Army of the Potomac and Corps of Engineers officer from the West Point class of 1846.
http://www.usace.army.mil/About/History/Historical-Vignettes/Military-Construction-Combat/033-Robert-E-Lee/