My votes went for
1.Big Chap
2.Aliens Queen
3.Covenant Neomorph
The original design is just so undeniably perfect and iconic. Every time it's on screen I'm mesmerized by it's design and movements. The Giger bio-mechanical elements really shine through the most. It's just amazing to look at. I love that Stompy is so closely based on Big Chap, but there's a couple of design elements that are bit off for me. Mainly stuff with the mouth.
The Aliens Queen is, of course, a brilliant and iconic design. But what really sells it is how good the practical effects and animatronics are for her. Still looks amazing and pretty lifelike today!
Realistically there's probably other designs I like more than the Neomorph (Stompy, Aliens Warriors, Resurrection drones) but I am just a big fan of the Neomorph in general. If for nothing else I appreciate how it mixes things up, and presents a unique and new design in the xeno lineup. It's very sleek and simple, but has some nuanced touches like the protruding jaw. I feel the same way about the deacon as well. While I have my loves and hates for the prequels, I'm a big fan of their additions to the xeno family!
Also, maybe a hot take, but I've always enjoyed the design and concept for the Newborn in Resurrection! I enjoy it's design and how it brings something new to the table, visually. Also conceptually the idea of a human/xeno hybrid, being born of a womb in a queen, and contrasting/mirroring Ripley 8, is really interesting to me. I just think that it's incredibly tacked on and comes out of nowhere in the plot, and ultimately not utilized to it's full body/cosmic horror potential.