Wendy,
Lob worms are the largest of the worms regularly used by anglers and can be up to three times the size of Dendrobaena. Dendrobaena are the mid-sized worm regularly used by anglers and brandling or red worm the smallest.
All will catch fish, used whole or in bits. Lob worms catch just about every species of note and used whole, tend often to sort out the larger specimens.
Brandling works well on all species, but particularly on shoal species like bream.
Dendrobaena are popular probably because they are most commonly available in tackle shops and will also catch virtually every species of fish.
This year, I caught my first and only catfish on lobs at the "catfish fish in" I've caught bream to 9lb 12oz on lobs, huge perch, pike, carp, tench and big roach on lob tails or whole worm and I've caught Salmon on bunches on lobs on a large hook.
Colin