ortlieb
 

cant say too much about other brands cause I have never used em.

I have only used ortlieb and as many others will tell you, they are very very tough, and very very reliable. If you go around the world you will have to fix almost everything at some stage ... the one piece of kit you will not have to fix is the ortlieb roll bag.

The 89 litre bag (XL) is HUGE ... and will encourage you to take a lot of stuff - too much stuff ... think twice before taking it. Probably weighs 20+ kgs full.

The 49 litre bag (L) I find a much more sensible size, and weighs about 12 kgs full. It forces you to have more packing discipline - and thats a good thing.

I have a ortlieb Large got it from Touratech.
which i have across the panniers & pillion can rest there back against, if they so wish, if just on my own length ways.