These guys have the two deepest resumes in the history of gloved boxing. Which of them was better is a tough call. If pushed though I would say that Sam Langford beat world class fighters over a wider weight range and did better against the same oponents even while past his prime. So there ith only one Tham Langford. He is not dead he is just on ice and when we thaw him out he is going to be prety pissed off.
Langford; his name should be synonymous with the concept of p4p perhaps even more than SRR. Greb ain't too far behind though, as most have already noted.
I have Greb a bit higher than Langford. This is due to Langford's being a bit too far back for my comfort -having begun fighting at least as far back as 1902. The bulk of Langford's bouts were before 1920 and that is the cut-off for me between "bootleg" boxing and the "early modern era" of boxing. Lanford had to ...compromise... more often and I can't quite draw a picture of his career in a way that I can be confident in its accuracy. Sam "Please Don't Call Me Boston Tar Baby" Lanford is top 10 easily anyway because I am very impressed with the extant film and the testimony of legions.
As long as you have both in the top two who cares. At that point you are about as special as they get.
I personally have them at 3 and 4. SRR and Armstrong are my top 2 but its pretty close between all 4 of them really.
To have them at 1 & 2 is crazy, how can you base this on fact. You are basing it on mythology because there is so little footage of them.
I base it on resume, accomplishments and contemporary accounts of both fighters. Even though there's no film of Greb, there is film of Loughran, Tunney, Walker and others that he beat. Langford looks excellent in what fight footage we do have of him.