The Punjab Worker in RFC, like the Fast Worker in CivIV, is one of the best UU's in the game, especially at normal speed. You can move onto a jungle, forest, or hill tile and start to work that turn. This normally translates to 15 or more extra worker turns per worker. There are a few UU's as good as the Punjab worker but not too many. And it never obsoletes, as JujuLautre points out. I would never vote the Fast Workers as worst, even at Marathon, where they're roughly 1/4 as good.
Musketeer is very nice in Americas or Africa. It's better in RFC than CivIV because of the natives.
Hard to pick absolute worst - there's the Ballista Elephant, Holkan is Dog (Soldier) food, Jaguar has same problem. Camel Archer is better in RFC because of the slight advantage you get right out of the box with your main unit. I'd have to vote Holkan - I never build one - I go straight for Shock Longbows.
Edit: 17% for Punjab Worker???
