Shredders and culebras are fine but the added stiffness of a puma would really help.  Pumas can really creek well.  Considering that full size rafts have descended the green and south silver, I think you would be surprized where your two thwart boat would fit, but if you want smaller, then the small size puma is hard to beat for the combination of stiffness, hole punching, durability, and manuverability.  Plus you could add a 3rd person.

As for those rivers you named, at the right levels I would do tellico, Little, suicide section, upper duece, island, or chick in a 13 footer.  Only rapid on suicide that wouldn't go is avalanche, all the others are raftable.  Telli would be a hoot at anything over 2 feet, little needs 3.5 plus feet, island needs a foot and chick would be really fun at over 2 feet.  Suicide would need to be about 8 inches min to go and cable would be a little scary.  I think pinball in a raft at 8-10 inches would be sooooo much fun.