The link to all three donation platforms they support/use is linked from the donation page that I linked in this post.
I've had a closer look at Liberapay after whay you said. It seems they don't take any cut at all. Liberapay itself is funded through donations. However, there are of course fees for the payment processor.
They also seem to accept several currencies, now I wonder which of these results in the most money in the devs pockets. The default seems to be USD, so maybe that? But could be the default because most people will prefer paying in USD.
Edit: hm, seems one of the two gets their payout in USD, the other in EUR...so I guess these are the currencies that work best.
To answer my questions:
So switching to USD from next month.