Hi, I've seen your other posts and….
I've got the OMM 32l,and the Gourdon 30 & 20.
Gourdon 30 is best for short bivvy excursions IMO 'cos it's robust, waterproof, spacious and has no excess of straps, mesh, & shockcord to catch on rocks and branches etc.
I bought the 32l OMM for a bivvy tour of the Tour Mont Blanc as I needed easier quick access to food, my camera and other equipment. I was also worried that the Gourdon's straps would be too harsh on my shoulders for a few days touring.
The OMM is better for carrying varying sizes of load, as you can compress it to fit the load. The gourdon tends to feel better the fuller it is. However, the OMM is made of more fragile fabric to give it such a low weight.
I use the Gourdon 30 for one night bivvys up on the moor, the OMM for longer excursions and the smaller gourdon for the ride to work 'cos it's too small to carry enough bivvy equipment.
Anyway, to summarise my erratic post, I'd get the Gourdon 30L if I was starting over again as it's cheap and ticks all the boxes (except the easy access to contents box!).