The best treaty?

As well as political and governmental deference to the Church. That was one of the causes of the Revolution...the supremacy and privilege of the Church and the Church hierarchy.

Wow... I guess it depends on how you define "best."

The Concordat between Napoleon and the Pope has to be in contention in terms of something that had a last effect on the greatest number of people for the longest time... Codified nationalizing church land, tacit religious toleration and ended horrible religious fracture in France.

The Treaty of Ghent between the United States and Great Britain that ended the War of 1812 is definitely in the running.

And Wellington had influence on how the treaty was done as witness his correspondence on the matter:

'I have told the ministers repeatedly that a naval superiority on the Lakes is a sine qua non of success in war on the frontier of Canada.'-Wellington.

Wellington further commented on the current diplomacy between the US and Great Britain:

'In regard to your present negotiations, I confess that I think you have no right, from the state of the war, to demand any concession of territory from America…You have not been able to carry it into the enemy's territory, notwithstanding your military success and now undoubted military superiority, and have not even cleared your own territory on the point of attack. You cannot on any principle of equality in negotiation claim a cession of territory excepting in exchange for other advantages which you have in your power…Then if this reasoning be true, why stipulate for the uti possidetis? You can get no territory; indeed, the state of your military operations, however creditable, does not entitle you to demand any.'

From The War of 1812 by Harry Coles, an interesting book that doesn't seem to be used much nowadays:

'The diplomats at Ghent accomplished little of a positive nature because the soldiers in the field failed to achieve a decision. Militarily the War of 1812 was a draw. Though each side was able to win minor victories on its opponent's soil, neither was capable of carrying out a large-scale, decisive offensive. What accounts for the inability of either side to achieve its objectives by resort to arms?'-255.

'At the beginning [of the negotiations] the British announced that their Indian allies be included in the treaty as a sine quo non. They also expected a cession of territory in eastern Maine and northern New York and between Lake Superior and navigable water on the Mississippi. A permanent Indian dominion to consist of all the Northwest behind the line of the Treaty of Greenville of 1795 was to be created. The right of Americans to dry fish on British shores in the North Atlantic, guaranteed by the Treaty of 1783, was declared to be forfeited, to be revived only by granting an equivalent.'-250-251

'The American commissioners had not the slightest intention of granting any of these demands…the British of course did not expect that they would be accepted. It was obvious to all that they were stalling for time and expected their armies in the field to accomplish what their diplomats at the conference table could never hope to do. Still the government did not want the negotiations broken off; they would yield just enough ground to keep the Americans talking. When news of the fall of Washington reached London on September 27, the British government had already decided to abandon the Indian buffer state. Completely confident of the success of British arms they suggested uti possidetis as a basis of settlement. Rejecting uti possidetis just as firmly as the Indian buffer state, the Americans again made ready to leave Ghent. Toward the end of October news of the naval battle of Plattsburg, Prevost's retreat into Canada, and the repulse at Baltimore reached London. Though shaken by these unexpected reverses the cabinet resolved to remain firm in their demands. Bathurst informed Goulburn that the military developments had not affected the government's plans, but 'had Lord George Prevost kept Plattsburg…we would have had a better case of it.'251-252.

'The cabinet might attempt to ignore the situation in America, but they could not remain indifferent to their own internal situation and the unending power struggle on the Continent. Prevost's retreat meant that the American war, which had already cost far more than anyone had contemplated, would have to be continued another year at an estimated cost of L10 million. To raise such a sum the hated property tax, due to expire within a few months, would have to be extended, and the chances of being able to secure such an extension were negligible. The war was an expensive nuisance in many ways. Because of the activities of American privateers insurance rates in the Irish Sea were three times as great as at the height of the war with France.'252

'Hoping a one and the same time to get Wellington out of Paris, where they feared for his life, and to rid themselves of the war, the British cabinet asked the Duke to assume command in America. Serving as ambassador to France since the end of hostilities, Wellington had long since become the cabinet's chief adviser not only on military matters but on nearly every important questions of policy. In reply, Wellington said he had no objections to going to America, but he could not promise much success there. 'That which appears to me to be wanting in America, or a general officer and troops, but a naval superiority on the Lakes.' Since a military solution was so unpromising why not simply end the war on the best terms possible, he suggested. 'In regard to your negotiations, I confess that I think you have no right, from the state of the war to demand any concessions of territory…Why stipulate for the uti possidetis? You can get no territory; indeed the state of your military operations however creditable does not entitle you to any.'-253.

Depending on how one defines best, Cintra should get a nod for best outcome by a negotiating team going in with very few good cards to play. I mean, it's one thing to stand on a raft and dictate terms having conquered half a continent, but to get an army out of the hole that Junot was in, complete with bag, baggage, and loot - that takes some doing.

Easy! The 2 connected treaties on 20 November 1815: Paris Treaty & Quadruple Alliance Treaty. But: the 25 March 1815 Treaty on Mutual Security is also an underrated one. Why? They continued allied cooperation in peace time and founded new system of collective security in Europe. That was really a novelty.

The Bourbons didn't last long and they had betrayed France and its people anyway in fairness