If you go with a plan, Kena and Iliad are by far the cheapest, but I have not seen a store sell them, they are usually online.
Vodafone is the most widespread in Europe. Just be careful, because what they offer for data usage in the home country, it will sometimes be less in other countries. For example, they will offer you 40 gb of data, but when in another EU country it might drop to 20 gb. Not a deal breaker, but better to know ahead of time.
I presently use Maps.me and they have many of the cycle paths where google does not. The only problem I found, was the GPS was not very accurate on the map. I was about 50 meters off and when on mountain trails can be very confusing. It may have been a one time thing.