They all add donors to lists and send them solicitations based on the premise that a former donor doesn’t need as much convincing for their cause. It’s fairly easy to unsubscribe as soon as you get the first message, but by then your email may have already entered a partnership pool, so you’ll start getting similar solicitations.
Best way around it is to use an email anonymizing service, or one way phone/text numbers. Or you can treat it like a game and donate under [email protected], then watch how many more messages you get to that specific address.
To answer your main question, eff.org and msf.org are pretty good charities. You can also check www.charitynavigator.org.
If it’s purely political orgs, local groups are less likely to have aggressive fundraising arms.