Whilst looking through my decks I noticed an interesting trend, I tend to include very few (often none) 3-cost allies.
There are only 2 of those who cost 6, Beorn and Brok. The latter seems very situational, the former less so but still hard to include in most of the decks. The cost of 6 is extreme though, so let us set it aside for now.
Surprisingly there are still only 4 allies of cost 1. But they're all super useful, I would go as far as saying that a majority of long-term players who run several decks have utilized most of the 4 allies in them.
Then you've got 2-cost. Spirit - having none of the 1-cost allies - shines in this dept. And it is not hard to make a deck that allows for playing one of these each round, building up a questing army. But other spheres have some great representatives here as well: Guardian, Spearman, Hammersmith, etc.
4-cost allies tend to be superb also. Haldir, Faramir, Tracker, Eagles of the Misty Mountains, these four may be among many players' favourites (and there are only 10 in total).
5-cost allies are even fewer, not surprisingly, so similar to the most expensive ones it is hard to look at them as a group. But there is Gandalf (and the new one coming) and Gildor, two game-shaping characters.
And finally you've got 3-cost allies, 16 of them! But for me it is hard to utilize them in my decks, they often seem too costly for what they do, and if I want to invest into an ally, for 1 more resource I can usually find a much more effective one among the more expensive group. Not saying they're all bad cards. Rivendell Minstrel may be the best of them though I still hardly play it. Mirkwood Runner is nice. Son of Arnor can be, and I have played that one a lot, but most of the games I only saw him being discarded. Dúnedain Watcher can save the day but there are swifter ways of dealing with shadow cards.
Do others feel the same or no?
ps: I wish Descendant of Thorondor had a cost of 3, we would then have an eagle for each cost from 1 to 5 (and Gwaihir coming as 6-cost perhaps).