my memory is that facebook is the lowest commision as they pretty much pass it all on but I can tell you as a charity receiving facebook donations its a real pita. They basically collect it all until you hit a certain threshold (about USD 150) and send it as a block then and then converted to your local currency at a sensible rate but a rate they don’t tell you so from a point of view of sending messages back to supporters thanking them for their donation it’s extremely painful
GFMs rates seem good to me as handling credit cards has a cost and their platform is well trusted so you are more likely to get people putting their credit cards into it rather than a platform they have never heard of. afaik they are also integrated with gift aid to make it easier. Assuming you make 1000 quid then 2% is only 20quid and I would happily pay that to get the data to me in a way that doesn’t take an hour to work out
But the best answer is probably to ask https://www.forgottenpeople.org/. What we did for someone who wanted to run a 20k for us was just fire up another web page on our site with their details and add a link to our donations page but tagged with their ‘project’. It integrated perfectly with our systems so there was no extra effort in receiving donations and we were able to thank everyone using systems we knew