[flak48]

In London, Citymapper shows the cost of each trip which can be very useful as there are often many routes that might take a similar amount of time but cost different (eg. sometimes you can take skip zone 1 for a few extra minutes or understand why you're paying extra when taking a train instead of tube in South London). It also recommends the best exit to take quite accurately for train/tube stations.

Citymapper is also much quicker to incorporate changed schedules and excludes delayed / cancelled trains from results within minutes of the changes being announced.

For altered schedules, Google is not only slower to react but also just posts a generic link to the TfL website - and you then have to parse the TfL notice yourself to understand which stations / bus stops are closed etc. The routes suggested by Google also still include cancelled trains / buses - it's your job to double check by visiting the TfL / train operator's websites.