They both have the same amount of trail, though they get to that end result differently since head tube angle and fork rake is different.
The AC has 4mm more bottom bracket drop.
The AC has 5mm longer chainstay.
The AC has more stack height for the same amount of reach(looking at the largest 4 sizes of each frame).
The AC's fork is cool because it has a flip chip to change rake. It can be 53mm or 47mm, depending on which setting you use. If you dont geek on geometry then this means very little to you.
Do these differences mean much to you? If so, take em into account. If its meaningless/unimportant, the dont.
Me personally, I geek on geometry and its the 1 thing on a bike that cant be changed out so its more important to me than which tires or seatpost is used. The biggest difference between the two is very much stack height vs reach. The Ribble is longer and lower than the AC.
As for frame quality- total toss up. The Ribble uses good quality tubing and will 100% for sure be overbuilt in order to pass fatigue testing in Europe. Same with the AC- it will not be slight in weight and the tubing they use is good, even if its branded as their own. Tire clearance is basically the same- 45mm for Ribble and 47mm for AC.
AC uses a 2x GRX build with a 46/30 crank and an 11-32 cassette and costs $2800
Ribble uses a 1x GRX build. You can get an Ultegra build though, but then its road gearing(though you can also get a 'climbers' gearing package) and costs $2640 in Ultegra Climber's option. You could spend the difference and buy a GRX crank and FD to get the same gearing as the AC.
If geometry isnt a big difference, then components sure are! Do you want 1x or 2x? That alone may push you one way or the other. If you want 2x, you can get road 2x for the Ribble and change stuff...do you want to do that? The Ribble in Ultegra Climbers option comes with a carbon stem, bars, and seatpost and you can choose from a bunch of tires.