Both can be used at the beginning of a yes or no question, you can use any of them. There are no specific cases to use one over the other.

Both of them are used to ask question and they are used interchangeably in many cases but أ has more cases that هل can't be used in or wider in usage than هل. Some examples: أزيد قائم؟ أ قام زيد؟ هل قام زيد ؟ هل زيد قائم؟ Look at أ in the following examples: أزيدٌ في الدار أم عمرٌ؟ This case only for أ . I hope this short answer helps you. There are many details I just wrote the main point.