All have subcommittees. If health care reform or universal health care ever became major issues, most of the committees listed above can claim some jurisdiction. This is internal power politics. All the more reason to get your legislator really interested. Unless yours is a purely local issue, you're better off dealing with the Washington office, which is more likely to have a specialist able and willing to deal with your issue.
Local offices are for individual cases or legislation affecting the home district.
A. Letters are definitely better, but should not be too long. Try to personalize your opinion. Describe your individual case, if applicable. Keep it to one page. Don't send a lot of written material.