I know you're full up, so I suppose you can only foster one.
I can't blame the girl bun for being nippy with the kids, although I've also learned not to take the owner's words at face value. If she's already allowing you to pet her a little that's amazing, much better than some I've worked with.
How was Pete btw?
If it really does come down to saving only one, IMO go with the one you think would be easier to adopt out for whatever reasons those may be.
What does your shelter do for advertisements? For example, my shelter has pet of the week pictures in local newspapers and sometimes they choose a rabbit. They also have a dog of the week thing at a local radio station (cause dogs bark into the microphone
where they will also mention other animals such as beautiful rabbits, baskets of kittens, specific breeds, or just how crowded they are for a specific type. Also classified ads for the shelter, partially to compete with the breeder ads in the paper. That stuff can help move animals but not all shelters do this for rabbits. If it's been so long since a rabbit was adopted, maybe you can convince them to advertise more? If it's a program they already do it wouldn't cost any more money.
Maybe try harrassing the HRS again to see if they'll return a plea for help for once...