Thanks for your support @dpoulton, that's always very much appreciated.
Good question, I've never looked into it before. Based on recent payments, PayPal seems to take on average 5%, while Patreon takes a total of 12%. It's more for Patreon because they have a flat 5% fee plus a variable "processing fee", which is to process the payments from the patrons, and in average it seems to be around 7% for me.
For now GitHub Sponsor has no fees but they will add processing fees in May, so it will probably be around 5-7% too.
I guess Patreon provides an added value, which is the recurring payments, and many people already have an account so there's nothing to setup is they want to support one more creator. There's also the gamification aspect of watching the monthly total increase 
So really it's up to you, of course I appreciate any form of support!