What's Advisable /Necessary / Preferable

What's Advisable:

You´d better do something quickly.
I´d better not add anything to my schedule.
I ought to do some wolunteer work
You ought to let them do the talking
You might want to takea collegue with you.

What´s Necessary:

I´m going to have to do something about it.
I´ve got to decide by next week
You don´t have to spend time on this.

What´s Preferable:

I´d rather (not) stay in my current job.