Boudica: horrible starting techs. Poor UB. So-so UU (Guerilla 3 is actually quite powerful). One poor leader trait with great synergy with the other and the UU. Boudica's the only leader with whom I've ever run a capture-the-AI's-cities economy. I'd call her low to middle tier myself.
Saladin: poor starting techs. Poor UB. Poor UU. One strong leader trait and one near useless (Protective). Close running contender for worst.
Churchill: decent starting techs. Ok UB. Ok UU. One strong leader trait and Protective. Some synergy between the UU and the otherwise useless Protective. Bottom tier, but one of the best of the bottom. (Haven't actually ever played him.)
Charlemagne: horrible starting techs. Strong UB. Poor UU. One weak trait and Protective. Another close running contender.
Tokugawa. decent starting techs. Non-existent UB. OK to good UU. One weak leader trait and Protective. Negative synergy between leader traits until you research rifling. Positive synergy between Aggressive and the UU - but it's nothing like Shaka. Negative synergy between Protective and the UU (why build Protective crossbows when you could build aggressive samurai?)
On the whole, I think Tokugawa just edges it, though Saladin comes close. Charlemagne 3.
I'm not a fan of Sitting Bull either, nor have I ever had the wish to play with Mao.
Saladin: poor starting techs. Poor UB. Poor UU. One strong leader trait and one near useless (Protective). Close running contender for worst.
Churchill: decent starting techs. Ok UB. Ok UU. One strong leader trait and Protective. Some synergy between the UU and the otherwise useless Protective. Bottom tier, but one of the best of the bottom. (Haven't actually ever played him.)
Charlemagne: horrible starting techs. Strong UB. Poor UU. One weak trait and Protective. Another close running contender.
Tokugawa. decent starting techs. Non-existent UB. OK to good UU. One weak leader trait and Protective. Negative synergy between leader traits until you research rifling. Positive synergy between Aggressive and the UU - but it's nothing like Shaka. Negative synergy between Protective and the UU (why build Protective crossbows when you could build aggressive samurai?)
On the whole, I think Tokugawa just edges it, though Saladin comes close. Charlemagne 3.
I'm not a fan of Sitting Bull either, nor have I ever had the wish to play with Mao.