Vertigo, interesting thread. Thanks for posting. I've not read all six pages of it, but I'll chime in anyway.
Commander. What does that mean? Commander in a battle? Series of battles? A Commander-in-Chief? A King?
In various battles and wars, the British have faced many nasty opponents. North Africa, sub-Saharan Africa, Central Asia, South Asia, East Asia, the Americas, Europe... The fact that the British have fought all over the globe is a testament to their many martial, economic, and cultural virtues/vices.
I cannot denigrate any of the opponents on this list. I'm only an amateur historian and I'll volunteer my view as such.
As for a battlefield commander, the British saw tough fighting against Ntshingwayo, Yamashita, and Rommel. As an American, I'm a big Old Hickory fan, but I'd like to add Daniel Morgan to this list. Even though "The Old Waggoner" suffered greatly from sciatica, he came out of retirement to fight for two years in the back country and rugged hills of the Carolinas. He is one of the inspirations for Mel Gibson's character in The Patriot. His outmaneuvering of Banastre Tarleton and his smashing victory at Cowpens saved the southern states, gave heart to the U.S. morale, encouraged the French to back us, and set an example for Nathiel Greene at Guilford Courthouse (a Pyrrhic British victory) that forced Cornwallis to retire to Yorktown.
Regarding an overall commander, I'd say George Washington. Of course, I'm severely biased as an American... and I just don't know the history of resistance in India like I do the U.S. Washington's brilliance was not on the battlefield. He knew how to identify able battle commanders and how to spot political appointees. Arnold, Morgan, Greene, Lafayette, and Von Steuben won almost all the battles for the Americans. Washington was smart enough to never get caught by the British. Keeping his army intact and as a poised threat bogged the British down for seven years. And the important thing is... he won. There was no Thermopylae. Thermopylae was self-sacrifice. Thermopylae was honorable. Thermopylae was legendary. Thermopylae was death. Washington survived and outlasted. I'd include Ghandi on this list.
Regarding a king or a national leader... I'd have to say Hitler. Napoleon was a threat, but not quite as immediate. Hitler bombed England, sank shipping, and assembled his forces. Churchill was forced to say, "We shall go on to the end. We shall fight in France. We shall fight on the seas.... we shall never surrender." France, Denmark, Norway, Netherlands, Belgium, Czechoslovakia, Austria, and Poland had already fallen. The Third Reich was an extremely real threat.
But as a combination... a battlefield general, a commander-in-chief, and an Emperor... Napoleon is it. The British battles in India, Afghanistan, Asia, Africa, and the Western Hemisphere were serious affairs, but none of them were a real threat to the soil of the British Isles. Those wars all were about locals resisting British dominance. As their next door neighbor, Napoleon put Britain to the test. I can't say anything that has not already been said... Who are the greatest British heroes? Nelson? Wellington? Well, then that tells you who the greatest enemy commander was!
I'd also like to say that even though the Britons are not the British, it's a shame to leave Gnaeus Julius Agricola off this list.
Edit: After posting, I read page six of this thread. I contend that Ghandi was not a pacifist. Pacifists are Quakers and Amish. Ghandi did not want peace. Ghandi wanted radical change, but without bloodshed. He knew the British Christian cultural values would win out if he refused to bear arms. By doing so, Ghandi forced the Brits to evaluate the situation with themselves as the oppressors... and that did not sit so well viewing the recent oppressors Hitler and Mussolini and the current oppressor Stalin. The Brits (and I contend any nation with Christian values) could not use force against people not willing to use force in return. Yes, and the Brits needed to recover economically.
Was Ghandi a military tactician? No. Did he lead men in a battle? No. Did he dismantle the British hegemony of his native country with a minimum of bloodshed? Yes. He achieved in a few years what India had not done in three hundred some years of British occupation. I say he was a brilliant commander.
The discussion has to be military strategy? What if it's just strategy? Isn't the guy who wins without losing a man better than all his predecessors who lost hundreds of thousands over hundreds of years? Doesn't the result make men who choose a military option look foolish?
But don't get me going on Ghandi's religious views and his betrayal of the Untouchables or I'll be here all day.