I will argue for Pete Sampras.

Since this is a four-round RootOff I'll just run down his list of accomplishments for now:
- 14 grand slams (ATP record)
-#1 ATP player for six consecutive years, record 286 weeks
-Won Wimbledon seven times and U.S. Open five times
-appeared in at least one Grand Slam final for 11 consecutive years
-earned $43 million in prize money (ATP record)
-64 career ATP titles (4th all time)
-Won at least four titles each year from 1990-1999
-ATP Player of the Year (1993-1998)
-Won 77% of his pro matches
-Won a grand slam in teens, 20's and 30's
-Won last grand slam he ever participated in (2002 U.S. Open).

The problem with Roy Emerson's grand slams is they were won against an amateur field. During this time, the world's top players turned professional and were unable to compete in grand slam events. The Open Era began in 1968, when all tennis competitors were eligible for the tournaments. Coincidentally or not, Emerson never won a grand slam after 1967. Also, three of the major tourneys were played on grass during Emerson's time, and that's Pete's best surface (proven by his seven Wimbledon titles). Consider how many slams Sampras would have if he faced amateurs on grass three times a year...

The competition level is just different nowadays. People will point at Pete's inability to win the French Open as a flaw, but there are many international players who compete only on clay and don't even bother participating in the other majors. Winning in Roland Garros is difficult for that very reason; facing professional-level clay-court experts is no easy task. Just look at some of the winners from 1993-2002:

Sergi Bruguera
Thomas Muster
Gustavo Kuerten
Carlos Moya
Albert Costa

None of them have won a Grand Slam besides the French Open, my point exactly. It's by far the most meaningless major, so although I'm sure you'll bring up the fact that Emerson won each of the grand slams unlike Pete, keep in mind how random those winners are and tell me how relevant such an accomplishment is.

Against the top-10, Sampras compiled a 114-60 record. Against players ranked 11-100, He had a 440-131 record. He played against 297 different people and had a winning record against 245 of them. Excluding players with only one career match against him leaves an even more impressive total: a 92% winning percentage with winning records against 141 of 154 players.

I never said anything negative toward Rod Laver. However, to say that was the legit competition Roy Emerson faced is a little misleading because Laver turned pro in 1963 and therefore did not collide with Emerson many times in his prime. Even with that said, in the open era Laver was 12-0 against Emerson. Also, Arthur Ashe was 12-1 against Emerson in the open era. That's a 1-24 record for Emerson in the open era against two of the world's best players. This is a sign that he dominated the amateur ranks and had solid success when he knew he had only one or two legit opponents. However, once the tournaments were open to the world's best, his play suffered and he seemed overwhelmed by having to face a top-notch player every round.

Just to enforce this point a little more, Emerson was never really the #1 player in the sport. While he dominated the amateur ranks, players like Pancho Gonzales and Ken Rosewall were winning big tourneys as professionals. For example, look at 1968, the first year of the open era. Emerson was the defending champ, but because Gonzales was now eligible, the two played in the quarterfinals and Gonzales emerged as the victor despite being nearly 40 years old and past his prime. How can Emerson be considered the all-time greatest when he never dominated the professional ranks?!

Let's not suggest Pete Sampras didn't play great competitors, either. Nowadays there are players of all nationalities and ethnicities. He had winning records against former #1-ranked players like Andre Agassi (20-14), Boris Becker (12-7), and Jim Courier (16-4).

Rankings are skewed by the fact that those guys won many tournaments on clay, so during that time period their point totals were pretty high. Anyway, Thomas Muster and Carlos Moya spent a combined 8 weeks with the #1 ranking, so that's not a big deal at all. It still doesn't change the fact that neither one of them won a grand slam aside from the French Open. It's by far the most irrelevant grand slam. Meanwhile you mention the clay specialists and their success, or lack thereof, in other grand slams.

1993 US Open
1993 Wimbledon
1994 Wimbledon
1996 US Open
1997 Australian Open
1998 Wimbledon
1999 Wimbledon

These were just a few of the grand slams mentioned in your argument because that's when players like Moya had their highest finishes. What do each of those specific tournaments have in common? PETE SAMPRAS WON THEM ALL.

You're not getting it. There's a difference between dominating amateurs and professionals, period. It doesn't bother you at all that Roy Emerson never won a grand slam once the open era started in 1968 and pros were able to compete in those events? The fact that he was never the world's best player makes it hard to believe that he's the greatest of all-time.

Ken Rosewall
-Turned pro in 1957
-Won 4 grand slams in open era
- 1968 French Open
- 1970 US Open
- 1971 Australian Open
- 1972 Australian Open

Rod Laver
-Turned pro in 1962
-Won 5 grand slams in open era
- 1968 Wimbledon
- 1969 Wimbledon
- 1969 Australian Open
- 1969 French Open
- 1969 US Open

These are just two examples of players who turned pro when Emerson was still an amateur. You mention that perhaps he couldn't afford to take the step, but that's just too bad. It's difficult to take his grand slam wins seriously when he avoided some very good players. Imagine if Laver and Rosewall were around during the 1960's; would Emerson still have 12 titles?

-Andre Agassi
-Boris Becker
-Michael Chang
-Jimmy Connors
-Jim Courier
-Stefan Edberg
-Ivan Lendl
-John McEnroe
-Mats Willander
-Patrick Rafter

All professional #1 players, and Sampras had a winning record against each and every one of them. He's one of three players to win two different grand slams four or more times. He was the world's best for a record 286 consecutive weeks. He also finished each year from 1993 to 1998 #1. This is dominance in the sport's toughest era, so I have a hard time believing tennis has seen a greater player in its life span than Pete Sampras.