If you use busses and trains often, there is a new flatrate: the so-called Deutschland-Ticket. It is a personal season ticket valid throughout Germany and entitles the holder to unlimited use of all means of local public transport. It is valid on regional trains (RE, IRE, RB, S-Bahn) in 2nd class. The Deutschland-Ticket is available as a personal subscription ticket.
With the Hessenpass mobil you can get the Deutschland-Ticket at a reduced price.
Tickets - overview
RMV tickets open up the entire network to you. They are valid for all modes of transport and services operated by the companies affiliated to the transport network. Children of up to and including 5 years of age travel free of charge in the area covered by the RMV network and cross-network fare zones. They must be accompanied by the holder of a valid ticket for the entire route.