This is yet another of those questions best answered by legal counsel and a CPA, neither of which branches of the professions is represented here. I 'd be willing to bet that only one personâ€™s name need be on the deed. I would NOT be willing to bet what consequences that might have.
The first issue you raise is that of a tax credit and what it means to the pair of you, jointly or severally. The credit itself is new and I'm sure that several bright-eyed individuals have had reason to investigate what it means, beyond the well-known fact that its eligibility expires as of December 1st, not 31st and that it is different from the 2008 credit deal of $7,500.00. The issue of who can and who should take this credit and at what time it should be taken is obviously an individual thing, bounded by who benefits most and what kind of a marriage you have. You have also somewhat mysteriously dropped the phrase, "Primary Residence" in-between the lines. To me, this indicates a certain amount of knowledge of divorce law but not a necessary sufficient one to make your own decision. Again your own marital situation would have to be taken into account, now at the planning stage and again, should for any reason a divorce became necessary. What is the primary residence, if down the road, you have three houses? Who owns what? Where did the money come from? (Inheritance might skew an "equitable" division, etc, etc.)
My advice is to look elsewhere for more competent advice from experts in tax accounting and marital law. Realtors are rarely equipped to answer this kind of question.
Best wishes with your new home.