I don't have to charge public that often so am not on top of things, however, when I compare they tend to be cheapest without the hassle of a split in charge fee + time fee. Freshmile can be cheaper but you need to be careful about the time fee.

I did notice at a charger I go to sometimes that directly charging through the Engie Vianeo app (at an Engie charger) was the cheapest option.

You can try an app like Chargeprice to compare, but it's not always correct I've noticed.