I have both.
Ko-Fi is good for people who want to make a one-time donation, and it's more streamlined than Paypal's donation system. You just click a link and it takes you to a page to make your donation.
Ko-Fi is also easier for creators to set up.
Like right now I can't even find a way to ask for donations clicking around Paypal's site without externally searching for directions. And the last time I used Paypal's donation button it looked like it was from 2004.
I like having both because if people want to support you on a regular basis, there's Patreon since I'm on a monthly system. If I just had Ko-Fi I would have to constantly remind people that I have it, and that could get annoying.
EDIT: And it looks like Paypal doesn't even do the donation button anymore? I tried looking it up but all you can do it seems is send an e-mail request for money and that's not the best …