Anderson, GSP, and Jones. One of those three will have the greatest impact ever. Fedor will always be remembered for his historic winning streak, but his lack of mainstream exposure, lack of top-ranked opponents compared to his GOAT peers, and the embarrassment of how hard he fell from grace despite not being very old will always hold him back outside of Sherdog-World.
Anderson was the first MMA fighter to be so successful that he earned BIG-MONEY sponsors, opening that door for others to follow and moving the sport's legitimacy into a whole new level. He broke nearly every UFC record ever and did so with a career full of artful finishes. He was the first MMA fighter to earn top-10 wins in 3 different weight classes, and he defeated the only other fighter to ever accomplish this so-far (Hendo). You could make an hour-long video of just his highlights! His winning streak ended in embarrassing fashion, and he needs to avenge that loss for his legacy, or at-least lose with dignity in the rematch.
GSP is the biggest draw in MMA history, working on his efforts to tie or pass many of Anderson's records. He is viewed by many as being nearly flawless in his technique. One day he may surpass Anderson, as he is several years younger and still going strong. The man has the MMA record for 50-45 scorecards, turning perfection into an art form. He is often criticized for his defensive style, yet he remains the most popular fighter of all time among mainstream fans.
Jones has unlimited potential, and already he is the undisputed GOAT of MMA's flagship division (LHW), passing HoF men like Chuck, Wandy, Randy, Tito, and Shogun. Jones has massacred every non-retired former UFC LHW champion in a one-sided beatdown. He beats strikers at striking, wrestlers at wrestling, and submits BJJ black belts. He uses attacks that nobody else can master, and he uses them to crush his enemies. He is technically undefeated aside from a BS DQ over an elbow he threw that wasn't actually illegal and that had no impact on finishing the fight (which ended due to shoulder injury from a takedown). His Nike shirts sell like Tiger Woods shirts, and he may well one-day be viewed as the Tiger Woods of MMA, known worldwide even by non-fans. He is 10 years younger than Anderson, giving him a ton of time to try and break all of his records (He already owns or ties several UFC records).
In the end, my money is actually on Jones having the biggest impact of them all, although Anderson has been my favorite fighter since the moment he became champion.
When mankind worships Infinity, it becomes without limits.
Fire is the ultimate element. It burns all. Even water. Anyone who says otherwise is just spitting out anti-flame propaganda.