I use Caradice and they can leak in torrential downpours. For this reason it is worth coupling them with rubble-sacks (heavy duty polythene bags you can get from the garden centre for a few pence). On the other hand I haven't had a problem with them going mouldy!
Ortlieb are completely waterproof, but not breathable, so the downside would be putting damp kit into them won't allow them to breathe. This may not really be a problem.
When touring I take Carradice and put clothes and cooking kit, tent etc in my panniers. My wife takes (more) clothes) and sleeping bags in her ortliebs as they are down and NOT something we want to get wet.
No idea about Jandds so perhaps not my most helpful reply to this forum. Ho hum.
c
