I've only ever done one via ferrata in my life, and it was les prises de la bastille which starts in grenoble and goes up the cliffs underneath the bastille. It's quite short, easily completed in two hours, with sections graded between AD and TD. Good, well maintained metalwork, good climbing (though some polished limestone, so don't do as I did and wear slippy old trainers) and gorgeous views over the city. Free too.
So that one has my very non-expert recommendation, especially if you have a half day in town with nothing else to do.