Taxation for married couple: Separate or Joint Assessment?

Hi,
I've been having a very frustrating time trying to figure out how I should be taxed.
We were married two years ago and revenue tell me that since then I have been taxed as married under separate assessment.

Now, I'm trying to figure out whether this is in our best interests or not.

Some background details:
My partner stays at home to raise our children, but does some part-time work. However the small amount she makes from it doesn't leave her liable for tax.
So, what's best for us in terms of tax status, separate or joint assessment?

What I'm basically trying to figure out is which will leave us paying the least amount of tax?
Many Thanks.

There are few if any circumstances where a couple are better off on separate assessment rather than joint. Normally where one spouse earns considerably more than the other, joint assessment is very beneficial.