Our great Civil War is simply crawling with great cavalry commanders. Harder than identifying great commanders of horse is picking out the poor cavalry commanders. From the beginning of the war to the end (better said- his end) Jeb Stuart is most prominent. He remained a masterful intelligence gatherer, screener, raider, and leader throughout and until his untimely demise. Remember that the development of the eastern federal cavalry caught up to his level and he did not regress to a lower standard. As the war dragged on, his resources in horseflesh, equipment, men, and forage was consequently impaired. He was discomfitted by Pleasanton's powerful cavalry force at Brandy Station it is true. His subsequent attempt to ride around the Potomac Army was unwise it is also true, but was not undertaken against orders, though undertaken a bit too eagerly so as to reclaim his command's preeminence. In my readings of Stuart, this raid is all I can find of poor decision on his part. His screening of Lee's army on its retreat from Gettysburg is again masterful. His handling of his corps, again until his demise, is the Stuart of old- masterful.
Forrest is nothing less than pure genius. Had he had greater responsibilities earlier in the war, one can only guess what would happen in the West. Certainly, the Union wouldn't have had things so much their own way. Grant, Sherman, and Hurlbut would have sent out whole armies to hunt him down. One disclaimer, I think Forrest rose as rapidly as one could expect. I think the real problem here was in how Forrest was used by his superiors. It wasn't until real late in the war that SD Lee or Richard Taylor gave him a wide latitude. Even Hood on his Tennessee campaign did not use him to greatest effect until the disastrous retreat from Nashville, in which case it was only Forrest (and some organized infantry units) to stand in the way of Thomas's pursuit.
Sheridan commanded infantry mostly in the war. His energy and drive though were perfectly adapted to the evolving philosophy of the use of cavalry by the North, and he was admirably placed by Grant and Halleck as the Army of the Potomac's cavalry commander. He counted on striking speed AND power, bringing to the east Forrest's maxim of 'git thar fust with the most'. His use of the cavalry to break Lee at Five Forks and then the pursuit to Appomattox is nothing less than brilliant.
Buford's defense in depth at Gettsburg and defense at Thoroughfare Gap are also brilliant. Wilson, Shelby and Van Dorn (when in command of cavalry) in the West are right up there in the highest echelon of commanders of horse. For continual efficiency of the highest order, Wheeler, Hampton, the Lee boys, Gregg, Merritt, and Kautz I can name. Surely many more can be named but it is time to close.
Regards all, ewc