I've ridden in the Vosges several times. I'm still amazed it doesn't get more attention with British bikers, who tned to rush past to the Alps...
The Route des Cretes runs north-south through the Vosges. It is a great road and although it gets popular with tourist traffic in the summer they give you something to overtake! As the name suggests (Cretes = crest) it tends to be fairly high up, which gives some great views. It is, in places, a fairly twisty road with some hairpin sections, but also some faster sections.
If you prefer the "up and down" nature of passes, just zig-zag east-west. The Col de la Schluct is a fine road, but gets very busy on sunny weekends - the car park at the top has hundreds of bikes. But I've never ridden a road in the Vosges I didn't enjoy (except Col de Bonhomme before they did the roadworks). You could send a couple of days within a relatively small area without retracing your steps too many times. There are proper mountain roads, some really twisty minor ones, and some faster bigger ones.
We've stayed in Gerardmer a few times, which has plenty of hotels and is fairly central.
When you head South from the Vosges there are some nice roads in the Jura Mts as well. Col de la Faucille is worth doing, and from the top on a good day you get amazing views over Lake Geneva to the Alps.
You'll enjoy it!