I suppose it's about what you want from your career, to be a health visitor you will need to be already an experienced nurse who then goes on to train further as a health visitor.
Social worker is not a job I would ever want to do, but then that's a personal choice, here is a link to the general social care council
which has some information about the job and training.
Mental health nursing, again not something I know a great deal about. I only did 12 weeks in my general training and that was in an elderly mental health ward. There is some great information on the NHS careers
you will need to sit down with as much information as you can about each job, and try to work out what you think will suit you best.