For JD it was Chris. It seemed natural – Chris was their leader, the hero, the personification of the West, the leader everyone with a lick of sense would be happy to follow. It was Chris who turned a bunch of misfits into the Magnificent Seven, Chris who made them a legend.
Ezra thought the glue who held them together was Buck. Buck with his heart, as big as Texas, his ability to make a fool of himself and made everyone laugh without bitterness, and his fierce loyalty no matter how loudly he called them all hopeless fools.
Nathan by that time had patched each one of them, including himself, at least once, and he'd come to believe that of all potential losses JD would be the most devastating. Of course, the boy had already seen and even done his share of ugly, but his innocence was still refreshing. He was the only one of them who just welcomed the future, and wasn't running from the past.
Josiah liked to muse aloud about fate and destiny and entwined paths, but one thought he kept to himself was that, in his opinion, they won't survive as a group without Nathan, and it wasn't just about Jackson's medical talents. Nate was the most level-headed of them, and maybe the only one who believed in greater good, while others just did what needed to be done or looked for adventure.
Buck didn't think about such matters very often, but when he did, he always arrived at the conclusion that Vin was the cornerstone of their team. His obvious skills aside, Vin had an amazingly clear head on his shoulders, and a very wise heart in his chest, though it took the rest of them some time to recognize the latter. And Vin grounded Chris, something Buck wasn't capable of anymore, if he ever had.
Vin was sure none of them was more (or less) important than the other, but sometimes he thought that the fact they lasted this long, alive and together, meant they had some powerful spirits on their side, and Josiah was the man who talked with them. Of maybe the Preacher just talked some demons out of chasing the Seven.
Chris was indeed a good leader. And as a good leader, he knew all the strengths and weaknesses of his men, and valued all of them. He also knew that if they tried to keep score, who saved the day and/or teammate's ass more often, there wouldn't be any winners or losers in that game. But if asked, he could answer that their secret weapon was Ezra. Lots of people in the West could shoot; some of them even did it for the right reasons. But those who could get what they needed without bloodshed just by talking and pretending, were rare. And those who were as good as Standish and did it for the right reasons were unheard of.
These were everyday opinions, which quickly (though usually temporary) got changed when one of them was in serious danger – of dying or leaving. The words were rarely spoken aloud, but the meaning was there – they were a circle, not a pyramid. Of course, sooner or later the circle would be torn, but as long as it didn't happen tomorrow, things were okay.