You should follow hubbers that entertain you, that help you, and that you interact with.
Hubpages is a place to learn. By following others, you will venture out of your box. Who knows what new information you can come up with. While it doesn't necessarily mean you have to read everything they write, following them will give you access to seeing what they write without having to go through all the latest hubs and hoping you come across them. If they wrote one thing you found interesting, chances are good they will write something else you enjoy.
Why should they follow you... because they like what you have to say. It is the same for why you should follow them. Does it mean you should follow everybody that follows you... not necessarily. But overall, someone following you is a compliment. It is because they like what you have to say and want to see more!