I am building a character for Hell's Rebels. I don't even know if I will ever get to play it, but I just love the heck out of it after reading through the player's guide. It's one of the first times where I feel a Noble Scion is a perfect fit.
What class would you say goes into Noble Scion most smoothly?
I was thinking Bard or Rogue.
I don't think there is a right or wrong answer, as long as your GM clears the whole "Leadership feat at level two" thing.
Though I would think twice about Bard. Since Dilettante Studies doesn't come into play with 5th level of the prestige class, you are going to have to slow your progression by quite a bit and then only pick an bonus to performance progression OR spell progression. Bard seems to be one of the few classes that are truly hurt with their split focus, as no other class seems to be truly split on what option to take with Dilettante Studies.
Bard would definitely be a flavorful choice (and who doesn't like Bards?), but just be aware that you won't get the actual 2 "pseudo-levels" from the prestige class ability. I'd just go with whatever concept you think you would enjoy the most (again, given the Leadership thing is cleared first).
You actually get to choose two Dilettante Studies, so you can grab both the performance progression and the spellcasting.