Unlike Nexus, Evolution's members weren't treated as backup to their leader. All of them were unique in their own way. Basically, what I'm saying is that each had their own gimmick.
First off, Triple H.
Still "The Game." The only diamond in professional wrestling. For the whole Evolution angle, he played the heel role to perfection. The calculating world's champion did any and everything to hold the world title. He beat every major RAW superstar at the time. The playfulness of DX was gone and Triple H was as serious as it gets.
Evolution's "Animal." The muscle-bound freak was undoubtedly Evolution's muscle. Multiple-time tag-team champion with Ric Flair. Batista defeated his fair share of main-eventers while in Nexus. (Like Benoit, Kane and Y2J himself.) Perhaps one of the most memorable RAW moments was when he returned and destroyed Goldberg, ending the assault in destroying Goldberg's ankle.
Then there's "The Nature Boy," Ric Flair.
Flair began as a lacky to HHH. But over time, Flair obtained a more prominent role in Evolution. The dirtiest player in the game played a major role in HHH winning/retaining the world title. He was also a mentor to Orton. Flair also helped Orton obtain numerous win's on his way to the top. Flair was the glue that held Evolution together.
Finally, "The Legend Killer," Randy Orton.
Orton was TOTALLY different than he is now. Obviously he molded to become world champion in the distant future, Orton was one of the longest reigning IC champions of this decade. Like the name says, he defeated many legends during his tenure. From HBK to Mick Foley, Orton was beating them all. His defining moment came at Summerslam in 2004, defeating Chris Benoit for the world title without any help from the others.
On to the Nexus. Besides Wade Barrett, what other members have showed they even have a gimmick or even a prominent role in the group? Besides beating down other Superstars? Thought so.