Y just received an inheritance and instead of spending the money right now, decides to put it away for the future. What annuity premium funding would be best in this situation?

Single.

Explanation:

An annuity is a policy insurance where the investment guarantees with a rate of return and it is tax deferred also.

In the context, Y decides to invest the money that he received as inheritance instead of spending it. Thus Y should invest in single premium funding because the single premium would ensure a tax deferred interest in the future.