Jehovah's Witness
The obviously essential teachings of the Watchtower organization should convince any interested person which organization is the one organization:
--- Exactly who is God? (Jn 17:3; 2 Thess. 1:7, 8, among others, show how essential such knowledge really is).
--- Who, alone, is proclaiming God's Name as He says must be done in the last days? (Ezek. 39:6, 7; Jer. 17:19-21).
--- Who, alone, is actively preaching the kingdom in the entire world as Jesus said must be done in the very last days? (Matt. 24:14; 28:19). Not all the nearly 1 billion members of Christendom combined are as active in "all the nations" as is the Watchtower Society, and no other organization even begins to approach the Watchtower organization in publications which further that "Great Commission." And certainly none of Christendom's organizations is actively preaching the kingdom message at all!
--- Who, alone, has come all the way out of Babylon the Great? You know, Babylon was a large city with very wide roads and huge gates. When Jehovah insists that all his people "get out of her, my people" (Rev. 18:4), he obviously does not mean for some to take a few steps toward the gate (or even only a hundred steps if they still haven't reached the gate and continued on out) and then stop! You must take all the steps required to retrace your entire route back along that broad, spacious road and on out through that huge gate, and then you must find the narrow gate and stay on the cramped road that leads to eternal life - Matt. 7:13, 14.
But what other organization has not stopped short of exiting that broad Babylonian gate? What other organization does not still retain at least some of those blatantly Babylonian doctrines/ ceremonies/ holy days, etc. whether they have taken a certain number of steps back toward that gate as "Protestant" organizations or not? Why, 99% of them can't (or won't) even rid themselves of the 3-in-one God concept which is so obviously part of "Babylon"! Or make any effort to uncover God's name which so many of them have knowingly helped bury!
-- Who alone has actually made a reality of the "one body ... one spirit ... one Lord, one faith, one baptism, one God and Father of all"? - Eph. 4:4-6. Who has really embodied a great crowd who sincerely strive for "complete lowliness of mind and mildness, with long-suffering ... earnestly endeavoring to observe the oneness of the spirit in the uniting bond of peace"? - Eph. 4:2,3.
This very solid unity or "oneness" which is so often criticized is, in itself, a necessity according to scripture (and reason). It is also unique among all the organizations claiming to be Christian today.
Of course you know that there are other important scriptural teachings which this organization lives by that other organizations either completely ignore or give only lip-service to. But when considering only these few essentials even, it becomes obvious that there is either only one organization today being guided by Jehovah's spirit or there is none!