I went for LoneRider MotoBags. I only use panniers for tours and wanted something definitely waterproof, would/should be fine in a drop or 2 & not huge when on the Bike. With Molle attachments i can add other bags/items to them for quick access too - handy for waterproofs, water bottles, 1st aid kit etc.
Just back from 8 weeks Nairobi to Cape Town with a biker mate using LoneRider bags. What a palaver loading and unloading them. In the evening we were all in the bar with a beer before Tim had managed to extract the inner bags from the clutches of the outer bags. In the morning we were still having breakfast whilst he was outside trying to reverse the process.
Whatever the question is, those bags are definitely not the answer...