Recently separated in Dec 2014. What is best way to file taxes ? Married but filing single, single or just what ?

If you were still legally married on Dec 31, and had not been separated for at least 6 months at that point, you must file as married. (As an aside - if you had been separated and not living together for at least the last six months you may have been able to file as Head of Household, if you met the other criteria for that filing status. But I realize that doesn't apply here.)

If you and your soon-to-be-ex can work togther to file jointly, that would probably be better for both of you than filing seperately. But if you can't (or won't) work together then you'll have to file a married filing seperately.

If you provide some more details, like how much YOU make, how much your spouse makes, any children, home mortgage, etc. we can give you a more definitive answer.

What ebaines says is totally accurate, but you really have not given us enough information with which to make good judgements.