TheBeak
When you say that you have passed the Army flying selection, I assume that you mean the Flying Grading Course at Middle Wallop. If so then you have done well. As a non-grad you will spend a higher percentage of your six years in flying posts than the grads and this flying experience will be invaluable in later life.
I suggest that you accept the sponsorship to Sandhurst from the AAC. You can always change your mind later on (you are allowed three choices if one of them is the AAC, two if the AAC isn't one). However, if you don't accept the AAC sponsorship then it is not as easy to change your mind as the AAC don't like being second choice.
Airclues