Over the years, the Sangheili have seen many design changes (some more drastic than others) in the Halo franchise. I did this with Cortana so I figured I’d do it again; In no particular order, my opinions are:
1) Halo: CE - There’s not much to be said about the good ol’ Combat Evolved Elite. He’s the one that started it all; this design laid the foundation for Halo’s most recognizable foe and cemented its look into gaming history. Tall, fearsome, agile, simply-shaped full-body armor design. Tech limitations of the age make it difficult to make out much detail aside from that.
2) Halo 2/H2:A - One of my two favorite designs, the Halo 2 Elite was basically the same guy as his predecessor with a facelift. With more polygons to work with, Bungie went all-out with detail, adding a more distinct facial structure, toned muscles, and more armor detail. The general physiology remained unchanged, but the concept of rank-based armor variations first came into play with the Honor Guards, Rangers, Ultras (I think? The white ones that look like Xenomorphs…) and the Heretics. All of the above is doubly true in the beautifully remastered Halo 2: Anniversary that came ten years later (although if I were to gripe about one thing it’s how fat, overly-numerous and weird-looking their teeth are up-close).
3) Halo 3 - I gotta say, not much of a fan of this one in general. They got kinda…chubby and stumpy-looking, its almost a bit comical looking back on it. I understand this was for multiplayer balancing and their overall design got the job done, but they looked far less like the proud, threatening warriors of before. Even something about the sizing of their armor just doesn’t look as cool as Halo 2’s Elites IMO, I dunno what it is. But Bungie did up the detail once more, adding more realistic skin and facial features, as well as more intricate armor patterns. There were also many cool new variations to wear in Multiplayer as well.
4) Halo: Reach - Tied with Halo 2 in my opinion, Reach returned the Elites to their scary, badass stature and design. They stood a fair bit taller than even the Spartan-IIIs, and simply towered over the average Human. They were again lean and ultra-muscular, with a slightly-altered foot shape and size that I personally preferred to the massive, chunky hooves of the past, adding to their sense of agility. The concept of armor variations was taken to new heights, making it easier to distinguish when you’re going up against a scrub or a Big Wig; and there are some HELLA intimidating designs. Where Reach falters is it’s general facial features; Smaller, beadier eyes, a rounder head and chubby cheeks mar an otherwise awesome physiology IMO.
5) Halo 4 (to present) - Very hit-and-miss for me. They kept the fearsome stature, but changed pretty much everything else. Their skin was made pale and scaley rather than dark and leathery, their mandibles became thin and finger-like extending up BEHIND their eyes, there’s a bunch of disgusting fleshy growths (?) on characters like Gek, and they doubled down on the huge hooves I never liked and made them absolutely massive. Also, the elegance of their armor was reduced to a sleeveless tank top armor…thingy with no undersuit on the upper body. They are definitely very well-detailed in Halo 5, and some armor variations (such as Jul M’dama’s) look incredibly cool. But the Elites underneath are simply too hideous and different to like for me.
6) Other (Halo: Legends) - As more of an aside, although I didn’t like how human the Elites looked in the animated short The Duel, I did kinda dig the tendril-like growths on the back of the Arbiter’s wife’s head. I know females are supposed to be nearly identical to males, but eh, what can I say?

I also like Halo 2 best because that was before lots of ugly, chunky, bulbous armor for multiplayer was introduced in force. I love their sleek appearance the most.