"We like to hike, so nearby trail access would be a plus."
ANY Rhine town will provide this access. It's an absolute hiker's paradise. Same goes for the train stations.
But it does pay to be "picky" about scenery. All towns within the Rhine gorge are attractive on some level, but St Goar (travelerguy's tip) and Boppard are at the top of the list when it comes to river scenery. Both of these towns have riverfront hotels with great views across the river:
ST. GOAR: Rheinhotel St Goar (some rooms with balcony) and Hotel Rheinfels offer great views and good proximity to KD cruise boat dock and the station. AND to the ferry crossing to reach the opposite riverbank. You can see both the KD dock and the tip of the ferry boat in the photo below, taken from the Rheinhotel:
https://dynamic-media-cdn.tripadvisor.com/media/photo-o/18/9e/0f/df/rheinhotel-st-goar.jpg?w=1400&h=-1&s=1
BOPPARD: Check out the Bellevue and the Ebertor (has both rooms and hostel rooms) for starters. There are others along the nicely-developed waterfront promenade as well, with several restaurants sandwiched in there as well. It's a slightly longer walk from the waterfront to the station in Boppard, but cruise boat docks and a ferry crossing are right there on the promenade as well.
The views in St Goar are better IMO. And Rheinfels Castle is right there in town. The ferry crossing there is a little handier than Boppard's since it's a short walk to the station on the opposite river bank for trips to Marksburg Castle, Rüdesheim, etc. AFAIK, there is just one small grocery store in St Goar (operated by the town.)
The Boppard waterfront is a fun, more active place with more options. Boppard is a larger town with multiple grocery stores and more going on including the Rhine's coolest chairlift. Visiting Rheinfels Castle is not hard from here since St Goar is only 10 train minutes away. Boppard has a much larger choice of restaurants in town. And as previously mentioned, the Guest Ticket is offered to every guest there once they've checked in. That covers most of your train/bus transportation needs during your stay, including trips you might make up the Mosel to Cochem and Burg Eltz, or further up the Rhine as far as Remagen. (Note that such trips, if you will be making them, will require a bit less time from Boppard than from St Goar.) Also: Boppard is served by direct RE train from FRA airport. Getting between St Goar and FRA will always require a change of train.
So generally, the game goes to Boppard, IMO, but St Goar is a great choice if you want to spend extra time just enjoying the river views from your hotel window or balcony.
Eltville and Rüdesheim: I rate these lower as travel base towns. Eltville lies outside the gorge (less natural scenery) and R'heim is a bit too touristy and generally less scenic as well than the other towns further north. Both are nice towns to visit if you have time.
Bacharach: A must-visit town for the half-timbered buildings there. But not really as scenic since the town is set back from the river too far for views, the exception being the splurgey Auf Schönburg Castle/Hotel at the top of the cliffs (not a good choice for train travelers, unfortunately.)
Oberwesel: Not as good a base town either... but a great hike exists from St Goar to Oberwesel along the clifftops, figure about 2.5 hours... and the remnants of the old town fortifications there make for a nice walk as well... use the Oberwesel train station to return to your base.
https://www.tripadvisor.com/Attraction_Review-g198501-d2189241-Reviews-City_Fortifications-Oberwesel_Rhineland_Palatinate.html
