If you desire to do a variety of rail trails, a hardtail MTB configured for comfortable upright riding with tires that are just a little more agressive than MTB slicks isn't a bad way to start. Suspension forks are optional depending on conditions on the trails that you ride. Most trails are smooth limestone surface but many have sections of heavy traprock and gravel with the occasional washout area. Rail trails are usually limited to under 3% grade so gearing can be more in the touring bike area. A 26/36/48 crankset ala many hybreds is usually fine.