Im a great fan of Gridcoin and SolarCoin, they are both PoS based, have 90 second and 60 second block times and altruistic goals that I think many charities would feel are in line with their basic ethos. They are smaller coins, but I think any charity would be well advised to keep most of their funds in fiat irrespective of whichever crypto they were accepting.
SolarCoin is on Lykke which creates direct fiat pairs for USD/CHF/EUR/GBP and both are on Coinomi.