Best App to get around a city?

I am very impressed with Citymapper . I have used that domestically as well as in Europe. If you're on wifi, it keeps up to date with real-time info on delays and traffic and multiple options for transport including walking directions.

I haven't had the opportunity to use it in those exact cities, but here is another vote for citymapper. I loved it in London so much that I have been using it all the time here in the Seattle area. It claims it is now in every major city in Europe so I think it should cover your selections.

i find google maps indispensable. i use android so i don't know if it's available on ios.

Citymapper is fine. Not as good as in London, as it might not have invested much in additional knowledge like which part of train to get on and off.

For Vienna I can recommend the app "VOR AnachB". It will show you the route from A to B either by public transport, or by walking, bicycle or car.

Especially for public transport this app is superior to any other app, as it had been designed primarily for that, having been commissioned by VOR (Verkehrsverbund Ost-Region) - Traffic Compound East Region (i.e. of Austria, an area of about 60 miles around Vienna).

Another person who agrees with Citymapper. A great resource. Obviously for bigger cities like London or Paris there are better options available, but this app works for most cities.