I was almost tempted to put 'leadership' in quotes but that would look like blatant author bias. However some of these guys were ultimately more useful to the Yorkists than they were to Margaret.
Henry Beaufort, Duke of Somerset (1436-1464)
This youngish man, son of the Somerset killed at St. Albans, was one of Margaret's better bargains, comparatively skilled in military and political matters. He had two younger brothers, Edmund and John, both of whom were eventually to die for the cause. His problems were his relative lack of land (as discussed in previous posts) and his limited experience. His advantages included a wide range of family connections, notably to the Earl of Shrewsbury and the rest of the Talbot clan. These links were by no means to be sniffed at.
Henry Percy, 3rd Earl of Northumberland (1421-1461)
Northumberland's father had also been killed at St.Albans. He seems to have been rather mediocre as leader of his family and had scant control over his younger brothers - though, admittedly, nor had his father before him. He had enormous influence in the north, but very little in the south, where it was perhaps more important. He was hampered by enormous debts run up during his father's time, not least as a result of the Percy/Neville feud which his younger brothers had inflamed.
Henry Holland, Duke of Exeter (1430-1475)
I have mentioned Exeter in an earlier post. Suffice it to say that even the Lancastrians had good reasons for doubting him and not all the time he spent in the Tower was at York's behest. He was very good at quarrelling with people though. He even tried to claim the duchy of Lancaster for himself which, given that Henry VI and his son were alive at the time, was the next thing to treason.
James Butler, Earl of Wiltshire and Ormonde (1420-1461)
Alleged by some to be the Queen's lover, Wiltshire seems to have been singled out for particular hatred by the Yorkists. He was high in favour under the Lancastrian regime and related to Somerset by marriage. His Wiltshire title was new (1449) but he was 5th Earl of Ormond with considerable lands and influence in Ireland. This may have been a factor in his getting across York and York's powerful Irish faction.
Thomas Percy, Lord Egremont (1422-1460)
Irresponsible and violent by nature, the kindest thing that can be said about Egremont is that he was probably a good chap to have next to you in a fight. He was Northumberland's younger brother. He was a leading light in the Percy-Neville feud that preceded his father's death at St Albans. He involved himself in Exeter's witless quarrels and for a time was locked up in London. Needless to say he escaped and eventually became one of Margaret's military supporters.
John, Lord Clifford (1435-1461) aka 'Butcher' Clifford.
He is famed for killing Edmund, Earl of Rutland after the Battle of Wakefield, apparently in revenge for his own father's death at St. Albans. Clifford was a ferocious fighter and quite prominent in Margaret's counsels. His killing of Rutland arguably stepped up the bitterness of the conflict and helps account for Edward IV's pretty ruthless killing spree after Towton. On the other hand, it was no worse than some of the other events of these wars and Rutland was no less a combatant than say the Lancastrian Prince of Wales at Tewkesbury.