payment processing fees

A donation page for a particular non-profit gives the option of donating via justgive.org, paypal, or bitcoin.

This made me wonder which one would be better for me to use from the charity's standpoint. Which one charges the charity the least fees, resulting in the most money for the charity?

For that matter, don't credit card companies themselves charge processing fees for each transaction? If these other payment processing organizations accept credit card payments, doesn't that mean that some fees are going to the credit card company, as well as additional fees going to the payment processor?

According to this page: Saving On Credit Card Processing Fees (dated Feb 2007),
the processor must pay a fee to Visa and MasterCard, which typically charge 1.65% for a normal credit card transaction.

According to the last comment on this page, some payment processors charge initial setup fees and monthly fees, in addition to the per-transaction fees.

According to this page (dated Aug 2011),
PayPal’s fees are smaller than either of the above options [JustGive and Network for Good], so long as the charity gets at least $3000 a month


Edited to add:
The video on this page explains bitcoins. It isn't what I thought it was (based on the name, I thought it was an official currency-backed micropayment service), and I'm a bit confused by it. It's a new artificial currency which anyone can "mine" by running a software program? Who are the people who exchange bitcoins for actual currency, or who accept bitcoins as payment, and what do they get out of it? It sounds sort of like the "money" you can accumulate in certain video games, and which you can sell to other gamers, except that its usefulness isn't limited to a particular game.


Edited to add:
I ended up using JustGive.org. One of their pages displayed this message: Please note that your credit card will be charged by JustGive and 4.5% will be deducted from your donation to cover transaction costs.

reasons

Reasons I post things online:

- to solicit answers/information on things I don't know
* to get answers

- to provide information to others
* to feel helpful & useful

- to entertain others
* to feel appreciated & useful

- to describe myself and/or my experiences
* to let similar people know that they are not alone & to thereby feel useful
* to get feedback from others; to feel less alone; to feel that others like me

- to express my emotions
* to understand them
* to remember them later
* writing about them helps the emotions to pass
(but why do I feel like posting those kinds of writings online?)
* to feel heard
(why do I want to feel heard? with emotional things, I often don't even want any feedback, so why?)
* to feel like I'm leaving a visible mark, no matter how small, on the world
(why do I want to leave a mark?)
* to transform emotional pain from something internal and transient into something external and permanent?
(buy why? what do I gain from it?)