@ Urcscumug lines of turrets generally fail. Aliens will jump on top of them and run along it chomping.
Not "aliens", goons. They're the only ones that can do this. Smaller aliens get pounded too bad if you have 3-4+ turrets firing at once. And rants can't jump the turret line.
** Actually they can, in certain situations. For instance, on Nexus a rant can charge up the stairs to the human base and jump at the top and it will land beyond the rets.
Alternatively it will just go melee at the corners so that only the turrets closest to the alien will attack it.
Or chew on the line until gaps are opened, which allow rants to pass-through. But:
* On ATCS, in the default base location, if you span the line of rets wall to wall there's no "corner" to attack.
* If you're pushed back in base and forced to defend against a smart AS3 team, you're pretty much screwed anyway. If they attack well the best you can hope for is a draw (assuming you're also S3 and depending on SD and TL).
* Curved lines (semicircles) are better in some circumstances. But they're also lines.

Against that specific goon attack (walking on top of rets) the best layout is scattering the rets around the place, both in the horizontal plane as well as at various heights. That's a great tactic, but you can't do it on ATCS. You need supports where to place the rets. The base on Tremor is a good example. But on the other hand such a base is weak against rants burrowing through the rets to reach other structures.
Personally I feel the best base is the one where aliens have a hard time finding which is the best way to attack it i.e. which is the weakspot that a single alien can exploit.
You seem to assume the best way to attack is with a single alien? What's wrong with aliens working together? In fact, they often fail if they don't.
This usually means my bases change over time so that what worked last round will not work this time.
From game to game, you mean? Unfortunately, the options are limited. Given a certain map, especially as small as ATCS, you only have few places where to make a good base. On ATCS the default location is pretty much it. Arguably, you can use the bunker and the tunnel, but that's a long way to move, which is something humans can't risk.
What is an awesome base the first time your opponents sees it may not be awesome the second time.
There are standard alien tactics and the answers to them are pretty much the same. Not to discount new ideas and originality, God forbid, but, especially on small maps, the options are limited, I repeat. Meaning that you don't have a lot of creative liberty as a human builder, and if you assume it you're base gets screwed very fast.
Additionally I always want my builds to require teamwork to kill even if that makes them a little weaker vs a coordinated attack.
Why are "teamwork" and "coordinated attack" on opposite sides in this sentence?
PS: Speaking of goons, I've noticed something peculiar about advgoons. They rely too much on their barbs and sniping and end up doing nothing else. I find it ridiculous, during an alien attack on ATCS, to see the regular goons jumping all over the place and attacking with everything they've got, while the advgoons, which are more powerful and have more HP, sit confortably around a corner, put out their head for a couple of snipes then run right back. Not sure what that's about. If that's how they're gonna use advgoon we might as well give the barbs to the advgranger.