What you're essentially looking for is simply a sorting algorithm.

Almost any will do.

Depending on how much IT experience you have (a layman for example might find some of the more advanced sort algorithms too complicated), you could just use somthing simple like insertion sort (for small lists it won't matter in practice anyway).

So e.g. using insertion sort for an A-F list:

1) Do you prefer A or B? (let's say the answer is B)

Now we know B > A. We try to insert C.

2) Do you prefer B or C? (let's say the answer is B)

3) Do you prefer A or C? (let's say the answer is C)

Now we know B > C > A. We try to insert D.

4) Do you prefer B or D? (let's say the asnwer is D).

Now we know D>B>C>A (we can skip comparing D to C or A). We try to insert E... etc.

One problem with Insert sort, is that the user would feel the questions are asked "in order". For a more "varied" approach, try maybe . Or if you feel you're up to it [url=https://en.wikipedia.org/wiki/Quicksort]Quicksort (sorry if you know about this already, as I said, I don't know how much IT experience you have).