If you are talking about land raider, I would say it was the ‘Grey Ghost’ (Col John S. Mosbey). He tied down a whole division of US forces to the protection of Washington, DC. He did run off with a lot of important US Army supplies to kept the Confederate Army strong enought to wage war (i.e. he did take off with about 4,000 US Army horses near Burk VA. He kidnapped a Union General during the Fairfax raid). If there was anything of value that was not nailed down, the risk of the Grey Ghost snatching it was there. At night, the US Army was compelled to retreat to forts and bunkers each night.
I’m with Agility Man staying with the Commerce Raiders of the C.S.N. however Raphael Semmes and the CSS Alabama sunk and burned over 64 ships between 1862-1864 before being sunk by the USS Kearsarge off Cherbourg, France. Alabama, Shenandoah and the other six commerce raiders succeeded in driving most of the U.S. merchant fleet off the seas by changing their flags ofr registry. Between Alabama and Shenandoah over 6 million dollars of shipping destroyed and another 3/4 million were bonded.
I can’t say what the questioner specifically is referring to but the term “raider” is usually referred to as a privateer (ie: authorized pirate) or a service raider designed to prey on merchant shipping. It usually doesn’t refer to cavalry (Forrest) or irregulars (Quantrill or Mosby).
The answer to your question is the Confederate raider CSS Shenandoah. She grabbed 38 prizes (but 21 of them were AFTER Lee surrendered at Appomattox, a full 7-8 months after the Confederacy fell). The raider captured over 1,000 prisoners and had only 2 casualties among its own crew (both dying of disease).
I agree with A Dull Man that Mosbey was great however my choice would be Nathan Bedford Forrest who seemed to be behind Union lines all the time with much bigger forces destroying communication and supplies and keeping Grant , Sherman and other Union commanders guarding their supply lines.
Dull Man beat me to it He was head and shoulders above the rest of them even Brown or Quantrell