Hi!I want to know the bet approach for the following problem:

I have to develop a system which has multiple users with different account types/groups say ( Admin, Doctor, QA, Clinic Account )

Common fields are:
Full Name, Email, username, password, account status.

Hmmm - sounds like you need granular control of permissions.

I am no expert on this, but I can tell you the following which may be good enough for your needs:

• JoomSuite (now known as Mighty Extensions) has an advanced user registration component which is much better than the core Joomla one and allows you to create various custom fields and so on. See here
• They also have a permissions component which allows you to set up custom types of account other than the core Joomla ones like Registered, Publisher and so on. You can modify access permissions to specific components and so on. As an example, you can even allow create a user groups to have front end access even when the site is offline, with or without ability to make submissions, whilst not having backend access - handy for demonstrating progress to interested parties whilst the site is still under development. See here
• These new JoomSuite usergroups are carried forward into JFusion, and you can assign which phpBB3 usergroups should match against your new Joomla usergroups. You can always create new phpBB3 usergroups if you need to (phpBB3 already has this functionality)

I use these components myself, though I haven't needed to play with special accounts and permissions too much yet. I find JoomSuite very good - the only drawback is that most of their components are encrypted with ionCube, so you will need that running on your server. Hope this helps.