MyAlterEgo, I would not consider Sampras as "dominating" for a decade, if you consider his results between 2000-2002, though his 2002 US Open win was great (one of my favorite Tennis moments).
After the 1990 US Open win, he didn't win another slam until 1993. So, his period of real dominance was 1993-2000 (7-8 years). Borg started his Wimbledon run and top notch winning percentages from 1976 and that extended until 1980, and 1981 (considering he won the FO and made 2 other GS finals, and of course no AO, but he won the Masters in early 1981 indoors vs. Lendl).
So that's 5-6 years for Borg of "dominance" so to speak, with an early retirement and Sampras at 7-8 years. So you have more years playing, which led to a larger total slam count, but Sampras was never a threat at the FO really, while Borg made 4 US Open finals on his worst surface.
So, look at these losses below at each of the Slams during their careers below. Borg's "bad loss" track record is superior to either Sampras or Federer, though one could argue that Borg would have had more bad losses late in his career. Maybe, maybe not, but he definitely left the Game with plenty of more great tennis left, although of course, if he played until he was say 29-30+, the inevitable physical decline would have occurred. Yet then, you'd also have likely seen more GS titles.
So, Sampras really didn't "dominate" much longer than Borg, and even with 4 slams played every year, he also won no more than 2 slams in any given year. I've posted this before, but let's look at the GS losses of Borg, Federer, and Sampras now, since we always tend to focus ONLY on GS titles when analyzing players. When trying to analyze the greatest of all time on each surface, it is useful to look at LOSSES as well as WINS/TITLES. So, I have looked up the track records of Borg, Federer, and Sampras at the 3 biggest Grand Slams. The Australian Open is catching up, but of course, the tournament was not really the same during the era of Borg and Sampras as it is now, even though by the late 1980's it had regained some past glory and Sampras did get 2 of his 14 GS titles at the AO. Borg's track record especially as far as "bad losses" is one reason I give him the slight nod over both Sampras and Federer as the greatest player overall.
Of course, for all 3, many of these losses were while they young and "upcoming stars", and I'm sure some occurred primarily due to injury (Sampras at the US Open, Borg retired vs. Stockton and was not well for 2 US Open matches vs. Connors, antibiotics 1 year, and a bad thumb injury in 1978 before the final).
This list of losses is illustrative of the fact that even these 3 greats get beat by lesser mortals from time to time. In my estimation, Borg was the most consistently dangerous/dominating player, considering all the surfaces, and he is underrated on grass/hard courts, relative to both Sampras and Federer. Also, consider his primary competitors, Connors and McEnroe (his 7-7 record vs. McEnroe was his worst head to head record, with no clay matches).
There is a dearth of bad losses (big upsets) against Borg even on the fastest surfaces. Of course, he and Nadal should be considered tops in terms of prowess on red clay. See the losses compiled below by Sampras, Federer, and Borg at what I'll call the "Big 3" Slams.
Bjorn Borg:
US Open:
Jimmy Connors (3), John McEnroe (2), Roscoe Tanner, Dick Stockton
(retired in 1977 due to shoulder injury), N. Pilic, and V. Amritraj.
Wimbledon:
Roger Taylor, I. El-Shafei, John McEnroe, A. Ashe.
French Open:
Adriano Panatta (2).
Roger Federer:
US Open:
J. Del Potro, D. Nalbandian, M. Mirnyi, A. Agassi, J. Carlos Ferrero.
Wimbledon:
R. Nadal, M. Ancic, T. Henman, Y. Kafelnikov, and J. Novak.
French Open:
R. Nadal (4), G. Kuerten, L. Horna, H. Arazi, A. Corretja, and P. Rafter.
Pete Sampras:
US Open:
Lleyton Hewitt, M. Safin, P. Rafter, P. Korda, J. Yzaga (2), S. Edberg, J. Courier, and Jay Berger.
Wimbledon:
George Bastl, R. Federer, R. Krajicek, G. Ivanesevic, D. Rostagno, Christo Van Rensburg, and Todd Woodbridge.
French Open:
Andrea Gaudenzi, B. Blanco, M. Philippoussis, A. Medvedev, R. Delgado, M. Norman, Y. Kafelnikov, G. Schaller, J. Courier, S. Bruguera, A. Agassi, T. Champion, and M. Chang.
