“Seaweed” has no consistent botanical/taxonomic meaning. What we call “seaweeds” belong to several different groups of algae, as well as regular plants. Any seaweed that is not too tough or crystalline to chew is also edible. Nevertheless some are better than others, and many need special preparation. Here’s three of the best:
This one is perfectly edible raw – a snack straight from the rockpool.
Also edible raw, but benefits greatly from long, slow cooking. Goes surprisingly well with red meats, and is best cooked in the roasting dish with lamb or beef. It will eventually disintegrate to a paste that tastes of monosodium glutamate, perhaps with some crispy bits.