Loses to all of them, although I think we could definitely see some surprises with Frazier and Foreman in a longer series.
Frazier really didn't like taking on shorter opponents, although he did it with surprising frequency. However, the 5'6"-1/2 Langford was around a solid 200 pounds for the filmed Jeannette X in Paris, and only had an inch less of reach than the 5'11-1/2" Smoke, who scaled 203-1/2 for Jerry Quarry I, his lowest peak weight. Sam's hooks were really effective at close quarters with Jeannette, and he'd much have the lower center of gravity in dealing with Frazier. I think this could put Joe on the back foot, and he didn't quite have the chin to support his style against Langford's particular brand of power, as Jimmy Cannon noted following Bonavena I. Heart gets Smoke to the final bell unless his eyes swell shut first, but he takes a few visits to the floor in the process and loses the decision. Ali could do what Jeannette tried with Sam in Paris infinitely better, and manage a pretty lopsided decision win. The nine inch height disparity between Langford and a stylist of Muhammad's speed, mobility, skill, endurance and durability is simply too much to overcome. The even larger Foreman is a different matter though. Defensively, he's wide open, a huge target, and much slower than Sam, telegraphing by Western Union. Stamina is hugely in Langford's favor. Wills was moving in for the kill when Sam cold cocked him with a single hook. We saw old Foreman take on an even shorter opponent with less reach than Langford in 1988, and Dwight Qawi actually managed to win a few rounds with guile and savvy. Prime Sam had considerably more experience than Qawi ever accrued, and was plenty shrewd. With the youthful Foreman of Jamaica, he'd move, bide his time, and drag George into deep water. If Foreman did have success cutting the ring off, Sam had the power to deter him before getting away again. Come the championship rounds, Sam would get him. George's deficit in stamina is too huge to overcome, and he'd be too slow to connect enough to manage an early win. For a period of over ten years encompassing more than 100 bouts overlapping his prime years, nobody halted Langford before the final bell, while the only significant display of power youthful Foreman demonstrated beyond round five was at the outset of round seven with Jimmy Young. He's not catching Sam in time to avoid gassing.
I also think he has the best chance with Smoke as well, if a man's in front of him he can counter pretty damn well i'd say. Foreman is harder to pick. I just don't know if he can weather the early round storm. Langford proved to be pretty damn durable over a lot of rounds, but it is george foreman...
the size difference would be too much for sam in all of these fights imo. sam's best shot would be vs frazier i think. it would be a great fight to watch for sure.