I've got the OEM panniers and a 52l Givi topbox, reasoning as follows:
Only use the panniers for touring and there's no frame left over the rest of the time, they are also pretty lightweight. Plus nice and narrow for filtering. When I'm doing anything more than mild off-roading I won't have the panniers on so their toughness isn't really relevant for me.
The 52l topbox looked ludicrously huge when it was on my garage floor, once mounted to the bike it looks completely fine. The size lets me store my helmet, lunch and any other equipment I need for work every day of the week.
Pretty happy so far but it's very early days!
Red M/T, the shinyness didn't last long...