Personally, I would prefer just using the two options("Mr/Ms"), so that there is no choice indicating marital status, and this is increasingly becoming the practice in many companies today. I've always though that if men don't have to indicate marital status in their title, then women shouldn't have to either.
But you should be aware that it is still fairly common to see the four forms("Mr/Mrs/Ms/Miss").
Also, please be aware of the potential problem that, since "Ms." is relatively new title for women(since sometime in the 1960s), it is still rather unknow in many parts of the world,
So, applicants may have to ask someone in your office what the word means.