Almost always panniers.
I find it hard to use a rucksac on the recumbent (well someone had to say it...)
I had a bike with no rack for a bit, and it just never got used. It's very rare for me to go anywhere and not need to carry something. Even if it's just to the village shop for a pint of milk, I still have to carry the milk. Once that bike had a rack, I could bungee the milk on there, or a cake, or panniers, or my jacket....
It's just inconceivable and pointless to have a bike that can't carry anything. Isn't it?