and Market Garden was an unmitigated disaster that he refused to take responsibility for right up to his death - even though he bullied Churchill and Eisenhower to make it happen and take the "shine" off that upstart Patton.
Monty took full responsibility for Market Garden, he just never said that it was an unmittigated disaster. He always maintained that it could have worked but didn't recieve enough support. Carlo D'Este states that Montgomery's admission of failure was unique: "the only admission of falure by a senior Allied Commander."
Eisenhower admitted it had been a failure only in private and had fully backed the plan going ahead from the moment Montgomery had presented it to him. He said later that "I not only approved Market Garden, I insisted upon it"
Montgomery himself said of Market Garden: "It was a bad mistake on my part – I underestimated the difficulties of opening up the approaches to Antwerp ... I reckoned the Canadian Army could do it while we were going for the Ruhr. I was wrong ............. In my — prejudiced — view, if the operation had been properly backed from its inception, and given the aircraft, ground forces, and administrative resources necessary for the job, it would have succeeded
in spite of my mistakes, or the adverse weather, or the presence of the 2nd SS Panzer Corps in the Arnhem area. I remain Market Garden's unrepentant advocate"
And, on a side note, Patton was never Montgomery's rival. Patton was only at an equal level of command to Montgomery in North Africa and Sicily but beyond that he never commanded at the same level that Montgomery did and didn't achieve the level of successes or failures (rare though they were) that Montgomery did. Patton has no great battle victories to his name (only El Guettar could possibly count) and his single greatest achievement was the turning of the 3rd US Army at the Battle of the Bulge but beyond that his accomplishment are no greater than any of the other American Army Commanders.
If Montgomery had a rival in the European Theater of Operations it was Omar Bradley - who commanded at the same level he did from the end of Operation Overlord onwards - but Bradley's success rate is not that good either and his judgement was certainly as suspect as Montgomery's was during the Market Garden Offensive - particularly, in Bradley's case, for the Hurtgen Forrest Offensive and the Battle of the Bugle and the advance to the Elbe. However I doubt whether Monty counted Bradley as his rival either.
The point being that Patton's place in the pubic perception of history as being Montgomery's rival who Monty was constantly trying to upstage is a complete fabrication. Monty accepted Patton's strenghts and flaws and considered him a good general and the best thruster in the Allied Armies and would no doubt have loved to have had him under his command at several periods. It was Patton who hated Montgomery, not the other way round, it was Patton who was constantly trying to upstage Montgomery and the rivalry Patton believed that they had was purely in his mind.