Butch had it out for Tony from the beginning. Once he had the opportunity to go after him and take him out, he did it.

No doubt about it.

Just my opinion so I want to hear your thoughts and opinions on if you agree or disagree.

Obviously we don't know FOR SURE what happened, but Butchie or someone from NY would be the natural choice. However, I think it's possible that it could have come from within Tony's own crew. Towards the end of the series, you can start to sense that many of his remaining guys are over him and have lost complete trust/faith in him.

I saw an interesting hypothesis that Pauline and patsy conspired… it was a novel interpretation

I agree with Rush. The sopranos were a skeleton of what they were in the beginning of the season. The only ally Tony had with the Lupertazi family seemed to be little Carmine. Coco had it coming for talking that way too Meadow. But Tony pointed the gun at Butchie. Butchie saw through John and The Shaw that the Soprano family was a thorn in the side. He had Tony get rid of Phil, because Phil was irrational. We only seen that one phone call where Phil tells Butchie that they're going to have a talk when things get back to normal. He was being a dick and kind of threatening in that phone call. Who knows how many other times he was a dick to Butchie. Get rid of Phil, get rid of Tony, and make peace with the rest of the sopranos that are left and bring them into the Lupertazi family. As Big Tuna mentioned, Tony's guys lost faith in him. At the end of the day, they all just want to earn and not be at war. War costs money and lives.