Well Federer and Sampras are interchangeable. I'll give you that. It's not as clearcut as Laver who is at another level.
I think Sampras > Federer. But I might be biased because I am a Sampras fan. You might think otherwise.
Laver is not clear cut as his 1962 slam was when the top 3 players were pro, and he was not - he only had Emerson in those years and none other.
To me Sampras was the most authoritative player I've ever seen. And it's not all about numbers. There are factors such as competition ( of the late and early 90s vs that in 2003-2007), Seeding system ( 32 vs 16 which made upsets more likely),
Sampras won 2 of his slams in 00-02 when the competition was not very good to say at least. Same goes for 96-99 when there were players like Berasategui,Korda,Kafelnikov, Washington winning or making finals at slams.
Not to mention Agassi being pretty much inconsistent in those years and not a regular #2 and biggest rival as Nadal is to Federer.
Agassi won 2 slams from 93 till 99 RG. He met Sampras the total of 3 times in those years. It's like Federer meeting Safin for the same time period.
nature of the surfaces ( less variation now with grass becoming slower and clay faster, meaning that one style of play works on all surfaces).
Yet we don't see Karlovic,Roddick making the RG finals, like Stich did. Can't see Delpo,Murray,Djokovic playing the same way on grass as they do on clay. Can't see Davy playing the same on grass either.
Not to mention that Sampras was an average player on clay so that's not something you can use to make your point.
A fair indication is a link between those two which is Agassi. Agassi who at age 34 recovered from a bad hip and nearly beat Federer in the UsOpen (took him to 5 sets) and aged 35 stretched Federer to 4 sets, even after being gassed himself playing a couple of 5 sets in the previous rounds. Agassi couldn't take more than a set off Sampras 10 years ago, and in all fairness, a 30+ Agassi would hardly have taken a set off Sampras. That tells me something.
The same Agassi who took 2 sets of Sampras in 93 Wimbey, and was eliminated by Flach, Martin and Haas the following years.
Not to mention Agassi being wank in 93 winning the total of 2 minor titles, not playing in the other two slams, and taken out by Enqvist in the 1st round of the USO. Not to mention Sampras being taken to 5 sets by juiced Korda in 97 Wimbey.
Federer was taken to 5 sets only by Nadal, Roddick, Haas(twice), Delpo,aforementioned Andre and Andreev on the road of winning 16 slams.
Sampras was taken to 5 sets by Corretja,Novak, Rusedski, Martin, Forget, Lendl, just in the USO(5 wins and 92 final)
It's not a science, and so results will be, of necessity, subjective. Do I think that Federer would have won so many Wimbledons if he'd played in the 90's, on fast grass? Would he have won 5 US Opens in a row, with Agassi at his peak, given how he struggled against a lame and ancient Agassi 2 years running. Who knows? What is clear is that Federer can't be the best of Sampras's era, because he never played then. Nor can we measure his career and then transpose it onto thoroughly different conditions of another era and say,he's the GOAT.
Um, lets see. Agassi during 94-98(04-08 was when Federer won his 5 USO) produced the following results at the USO:
94:Won(taken to 5 by Chang, beating Muster,Stich, Martin(not exactlly world beaters at the USO))
95:F - taken to 5 sets by clay courter Corretja.
96:SF-straight setted by Chang.
97:4th Round exit to Rafter
98:4th round exit to Kucera
So Agassi in those years was a non factor in 3 of them.. Not to mention being much more inconsistent than he was in his latter years - (between 99 and 05 he lost before the QF on only 1 occasion.). Not to mention that this lame and ancient Agassi had won 8 slams by that time and the time Sampras met him in 95 he had like 3?
Not to mention Agassi being non existent in 94 and 97 AO when Sampras won there. Not even in the draw.
That would be only opinion. I think we can say "he's the best we have seen", or the best of his era, but I'd be skeptical of anyone who would look at this generation and then look at the last, and be comfortable saying that one player was better than such a great player as Sampras, given how different their careers were.
Um, lets see, the only multiple slam winners in the 90's were - Edberg, Agassi,Courier,Bruguera,Becker,Kafelnikov,Rafter
Edberg won his before Sampras's domination, same can be said for Becker and Courier, with the former winning 1 slam post 93.
For those in the 00's you have Kuerten, Agassi,Sampras.
For Kafelnikov and Rafter you have Hewitt and Safin who both I think are better and of course Nadal's 6>Agassi 5.
Granted the conditions were different and it would be hard to compare.
What we have for sure is the records. And soon Sampas would have no record left to his name.