Depends on how much of a challenge/sport you're looking for, and what kind of flies you'll be offering them.
A lightweight 2 or 3 weight rig using little bitty flies at the end of gossamer leaders makes the game a little more technical/challenging, and a decent size bluegill can feel like a decent size trout on a heavier rig. It's the way I would go.
If the intent is to fill a stringer of fish no matter what, go with a 5-6-7 weight outfit with a thick heavy leader, toss poppers/streamers/terrestrials at them and horse them in.
