Hi! I would suspect your questions have been asked & answered in the Newbie Comic Collecting Questions forum - you may want to check there for (better) answers. I think, ultimately, it comes down to your personal preference. You can also google search acrylic vs oil-based vs permanent inks.
I recall seeing an article about Sharpies and how darker inks (black, blue) and metallic inks tended to do better over time. But even they still faded. I think it even says on the packaging that Sharpie metallic inks are fade resistant - not fade proof.
And I think oil-based inks are fade-resistant??
For acrylic paint pens, I personally think they do tend to look better - the colors seem to "pop" more than a Sharpie signature.
I know that how porous the item being signed is also something to consider for different kinds of pens/inks. And the "flow" of the ink is something to consider too. I saw a celebrity use a black pen (I think it was oil-based) to sign a poster (it looked like glossy card stock to me) and as he started to sign it, the ink just flowed out and bled everywhere - it literally left a little pool of ink on it. I also know a creator used a non-Sharpie pen to do a remarque on a bronze age cover and a similar issue happened - once he started to push down on the tip, too much black ink unfortunately flowed out onto the cover causing smearing.
I believe acrylic paint can also chip?? So, could a thick acrylic signature inside a slab chip? I guess anything is possible, but I don't remember hearing of this actually happening.
With all that said, I'll go back to my disclaimer at the beginning and suggest that you check out the Newbie forum for better answers!