Preface: Both makers are amazing. I've owned 3 different AP sets, and I've helped build 2 others. I've helped build 2 RS builds, as well as knowing 3 people who actively troop in one. Either choice is gonna be perfect. Everything below is my personal experience.
I think the AP ABS is thicker. Honestly AP might be one of the thickest ABS pulls out there. This leads to softer pull details in some spots, but it does make it super resilient to trooping damage. I've only developed 2 cracks in my crotch tab, and that's because I sit down in armor because I'm a lazy person. I've been actively trooping in my main trooper costume for 3 years now.
I know of one trooper in my unit who has several chestplate cracks on her stormtrooper from RS. She uses a bracket system though, and that will put extra stress on areas. I think most cracking with any costume will be mostly based on how your treat it and how well you distribute stress.
There's a slight difference between the RS and the AP ABS. I find the RS ABS to be a slight off white. I've not compared to a PVC kit.
I've not seen yellowing issues with either. My AP ABS is still stark white after years of trooping.
I have zero experience with PVC, but have heard drawbacks to it and that it is more prone to cracking. Don't take my word for it though.
You're gonna be fine with either kit at your size and weight
Two things to note about the AP/RS. The RS helmet is slightly bumpy like the original screen used helmets, and is probably the most faithful to the original for that reason. The AP helmet is a smoothed and cleaned up version of that, so if you don't like the bumps that's probably better for you. However if you're super about those movie accurate bumpies, then RS will suit better. The thighs between the two also look a little different to me, so preference there.