Aurelion: Max W First
I appreciate that q gives a nice stun and posts bigger base numbers, but please max w first. You won't be building much if any CDR on Aurelion, and W does far more dps. It also provides tremendous protection on the form of zoning. Notice its cooldown lowers so much; that is a hint that this skill is not a 1-point wonder. Use it like a projectile. Remember that once you finish rylais, W = death or flash if you catch someone out with it.

This is the perfect Aurelion build. Almost all your damage is from W. The only purpose of R and Q is to help you kite and zone into outer orbit.
edit: mejai's is there for the movement speed which synergies so well with AS's kit. If you aren't confident at maintaining at least 15 stacks, pick something else like zhonyas or abyssal.
would actually be very strong on Aurelion. His base ms is so low, but the 60 ms from momentum stacks would work very well with his % movement increases and greatly increase kiting ability
is activated by W, I actually prefer it over Luden's right now on PBE. Both work well, so it's personal preference.