Same thing when speaking it out loud. 'B four D capital Q B capital F s thirty-one' is way more convoluted and error-prone than 'B four D Q B F S thirty-one'.
The best thing I've found that fits this criterion is Crockford's Base 32 [1], basically the extension of hex digits, removing letters ILOU.
But Base 32 (case-insensitivity by proxy) constrains us to 5 bits, which is only a 20% reduction over the 4 bits of base 16. So instead of the 20 bits `1ab2f` we could express them with something like `1qm3`.
Or we could be using words...