If you had one tour to take in London. Would it be Charles Dickens tour, Sherlock Holmes tour or jack the ripper tour?
Are they all by one company?
no, different companies
Well, then I guess it would depend on the company and what they offer.
I've looked at the London Walks tour of Charles Dickens' London which looks good to me. I've done a walk with Richard III (Highgate) and he is very good. http://www.walks.com/London_Walks_Home/Fridays_Walks/default.aspx#12893 I did do a tour in London a few years ago and the guide took us on a walk in Southwark which is some of the area which Dickens used for Little Dorrit and where Dickens' father was in debtors prison. We also went to the museum in his home (or one of his homes?).
Here is their search for Charles Dickens.
I've also looked at their Sherlock Holmes' walks which might be interesting.
I would choose the Jack the Ripper walk last. I did it years ago and it was not that interesting.
I took 3-4 London Walks and all were excellent or better. Their website gives a lot of details on the tours and the guides, so you can get a good idea of what is likely to appeal to you.
I have done a Jack the ripper tour and it was very good, but would probably choose the Charles Dickens one.