Double shot or not, it's still ABS: shiny happens
PBT will definitely take longer, it's a harder plastic
Harder and more corrosion resistant! (POM is another option, but all the POM I've seen is pretty smooth to begin, so PBT wins again)
I don't mind ABS at all. PBT do hold their texture, but they also get dirty really quickly. It's like they are cleaning your fingertips. Even if you wash your hands before keyboarding. If they collect any dust at all, you will forever be cleaning your PBT caps.
This has not been my experience. For example, my unicomp has never been cleaned, and I've typed on it every day since Dec. 2010. My SP PBT keycaps got a little dirty, but that's because it addition to never cleaning it, I often ate over it, and it's right under my head, so dandruff happens. This has also been the case with my current ABS keyboard.
Thick doubleshot ABS plastic looks nice, but it' can't beat PBT in feel. I also contend that Dyesub PBT legends can be easily made not blurry. Portal round1 is a case in point.
Go PBT.