Best stamina - Felix Trinidad. In the final rounds he was like being in the 3 or 4. I remember his team said he recovers, between rounds, in less than 30 seconds. Remember the 12 round against Vargas and the 11 round against Reid. Worst - Taylor, Pascal, Sometime De la Hoya.
Yes Trindad had tremendous stamina. He would throw bombs for 12 rounds. And for a big puncher he was quick. Duran another fighter who had freakish stamina. I put Calzaghe in the great stamina department as well. It's a shame some folks give him a bad rap for being a slapper. He wasn't like that in the beginning of his career before his hand injuries.
Right now, among top fighters Best: Timothy Bradley Manny Pacquiao Austin Trout Paul Williams Worst: Zab Judah Jean Pascal Bernard Hopkins (sorry folks - his stamina used to be great, but it's been pretty crummy since the Taylor fights) David Haye Not sure if Cirstobal Cruz is still a top fighter, but his stamina is pretty insane too.
Fighters like Pryor, Williams, Ouma, Margarito, all had great workrates and could generally keep it up for all or most of the fight. Arguello scored his share of late stoppages. Ali got the hell beaten out of him to the body against Foreman and Frazier (another guy with great stamina). It's amazing that Ali finished the Thrilla so strong after that body punishment and the heat. Leonard had great stamina too. The late finishes of benitez and Hearns. He finished stronger than Duran in Montreal despite taking a hammering to the body.
You can't mention worst stamina without Shavers tho. His stamina is sooo bad that's one of the biggest reason he gets knocked out a lot.