I just got the arekel UB, and so far i like it a lot. The hard back that extends to the bottom of the bag means that it won't sag when you load it down, and the top pocket is great for items you need to reach quickly, or items that need to be protected (it also has the hard bottom) like eggs.

Since i received the UB i took it for an overnight trip as well, and think that it could easily fit enough gear, clothes, and food for a few nights if traveling light. Strap a tent and sleeping bag to the top of the rack and you are ready for some bike camping...
As far as water proof goes, you can always just buy a water proof cover for whatever pannier you choose.

That's my contribution, but i think you will be happy with whatever you choose. I have to say that i am a convert and i sing the praises of panniers to everyone, it feels so good to get stuff off my back.