I like having Darwin on the £10, but I'd like to have Turing on a note as well. Maybe the £5 would be better, though that would mean getting rid of Elizabeth Fry, who I believe is the only woman currently on the currency (except Her Majesty of course), which may upset some people. The other options are the 20 and 50, which have Adam Smith and Boulton and Watt, respectively.