Gelbooru is pretty good if you have adblock and a stomach, since their porn intermission/pop-unders (Who the [tornado fang] uses those?) are gag-worthy.
Safebooru has none of that IIRC.
If it's scat or guro pop-up/whatever, I'm staying the [tornado fang] away from it.
Also adding to Safebooru, usually anything past "PG" gets deleted from the site, though the mirrors to the other 'boorus might be there if it's posted there. Not sure if Sankaku Complex has pop-ups, but has Gelbooru's flexibilty of 18+ images.
And speaking of ecchi, I could swear some people have found some good Pokemon ecchi somewhere but don't know where...