|The Babe modeled his swing after Shoeless Joe: I'd say it worked out pretty well for him|
Almost 80 years after he retired, Ruth still has the highest slugging percentage, OPS, and OPS+ in baseball history. His .474 OBP is second all-time (behind the next guy on this list) and his 714 home runs rank third behind Barry Bonds and Hank Aaron.
2 Ted Williams 190 OPS+ 188 wRC+ .493 wOBA 1,069 Rbat
Williams wasn't the greatest hitter who ever lived, but he came damn close. Had he not lost nearly five seasons to military service, he probably would be. His .482 career OBP will likely never be topped.
3. Barry Bonds 182 OPS+ 173 wRC+ .435 wOBA 1,129 Rbat .353 TAvg.
Whether people like it or not Bonds is the all-time home run champion. He also has more walks than anyone else. He had an OPS over 1.000 every year from 1992 through 2007 except one, and in the year he missed (2006--his age 41 season) it was .999. Most impressively, he was an above average hitter (by OPS+) in all of his 22 seasons, and was still going strong (1.045 OPS at age 42) when baseball shut him out of the game.
4. Lou Gehrig 179 OPS+ 173 wRC+ .477 wOBA 971 Rbat
Gehrig was a machine before ALS tragically curtailed his career. One can only imagine how a healthy end to his career would have played out and what his final numbers would have looked like.
5 Ty Cobb 168 OPS+ 165 wRC+ .445 wOBA 996 Rbat
Cobb's career average is .366, which he maintained for 24 seasons. He won 12 batting titles in 13 years, and in the year he didn't win he batted .371. And though he retired before the Great Depression, he still ranks second in hits, runs, and triples.
6 Stan Musial 159 OPS+ 158 wRC+ .435 wOBA 885 Rbat
The Man was the National League's answer to Ted Williams throughout the 1940s and '50s. He was so consistently dominant that he pretty much led the league in something every year into the late '50s, and his 1948 season is one of the best single season performances any hitter has ever had.
7 Tris Speaker 157 OPS+ 157 wRC+ .436 wOBA 819 Rbat
A slightly lesser version of Cobb, the Grey Eagle roped 792 doubles--most all-time--and batted .345 in his 22-year career. Had his career not overlapped with Cobb's, he certainly would have won more than one batting title.
8 Mel Ott 155 OPS+ 156 wRC+ .430 wOBA 775 Rbat
One of the best young hitters in baseball history, Ott posted a 1.084 OPS at age 20 and remained an elite hitter through his mid-30s. Few players have ever taken advantage of their home park as well as Ott, who tailored his swing to fit the Polo Grounds (where he hit 323 of his 511 home runs--63 percent) and won six home run titles in an 11 year span.
9 Johnny Mize 158 OPS+ 157 wRC+ .433 wOBA 505 Rbat
The Big Cat has been largely forgotten by baseball history, but at his peak he was one of the most lethal hitters in baseball history. He batted a Joe DiMaggio-esque.324/.409/.588 over his first ten seasons, which included a three-year interruption because of World War II. Also like DiMaggio, he hit for power (359 home runs) and rarely struck out, whiffing in just 7.1 percent of his plate appearances.
10 Shoeless Joe Jackson 170 OPS+ 165 wRC+ .443 wOBA 439 Rbat
Banned from baseball after one of his finest seasons, Shoeless Joe was well on his way to a Hall of Fame career. As it stands, his .356 batting average is third-highest of all-time behind Cobb and Rogers Hornsby. He only got to play one season in the live ball era, so it's interesting to speculate how his numbers would have turned out had he lasted through the 1920s.
Honorable Mentions: Bill Terry, Jim Thome, Eddie Mathews, Tony Gwynn, Wade Boggs, Larry Walker, Ken Griffey Jr.