Rhine Romantic Route (drive,train/bus or cruise?)

The "romantic" part of the Rhine lies roughly between Koblenz and Bingen. If you're there for a short time you can get along fine by train - there are tracks on both sides and trains stop almost everywhere - and you can cruise the river too if you find that interesting. There's no reason a car won't work if you prefer that.

If staying over - and you should - pick a town in the heart of things. St. Goar is good because of its gorgeous setting and the ferry there that allows access to a train station on the opposite side of the river in St. Goarshausen. Tour Marksburg Castle in Braubach to the north (walk up from town or take the little shuttle from the middle of town.) Take side trips to Bacharach, Boppard, Oberwesel, perhaps Koblenz.

See www.k-d.com for cruise boat schedules.

I'm not sure how active you want to be but there are also long-distance hiking trails on either side of the Rhine that make for wonderful outings, especially in the fall (late October) when the vineyards are all changing colors. The trail leads you to some of the castles along the river and down into the towns as well, so you are never far from civilization. Worth looking into, for sure.

I agree with Rick about cruising from St. Goar to Bacharach (or opposite direction). It's the best use of time and money. The train that stops at both is a good ride through the rest of the section.

I've gone this way and driven. IMO if you don't have another reason to get a car, use the local train - get off for the cruise - then hop back on the train.

The cruise is slower/longer upstream than downstream. If you have time go upstream, if you're pressed choose downstream.