I have one addition and one correction:

1) Rapid shot allows you to target different opponents, whereas manyshot must hit the same target.

2) rapid shot is usable with any ranged weapon, manyshot only applies to bows. It is not stated explicitly, so it's not clear if you must choose a specific ranged weapon when you select the feat or if you can rapid shot with any ranged weapon. Compare with Rapid Reload which requires you to choose a crossbow type. As written, you could rapid shot with a bow one round, then two spears, then a hand axe and a dagger!