Personally I find the most creative letter as ‘O’ and most creative number as ‘8’. Because letter ‘O’ is an artist that can give form to many letters like small ‘a’, ‘p’, ‘b’, ‘d’ and ‘g’ and capital letter ‘R’, ‘P’, and ‘B’. Also letter ‘O’ contains ‘C’ within it. However you can’t ignore letter ‘I’ as it is equally creative giving base for letters like l, h, b, q and many. But alphabet ‘O’ wins the race as it looks like zero ‘0’, a number, so letter ‘O’ can be called as a double featured letter or a camouflage letter.
Similarly, talking about number ‘8’, it contains even the alpahbet ‘O’ and contains in itself number from ‘0’ to infinity (the number ‘8’ shifted clockwise or anticlockwise to 90 degree gives infinity). Also ‘8’ which contains two ‘0’ is the base for numbers like ‘6’ and ‘9’.