Well, since you included both chrons

I had to go with Sunder, hands down. His strength, his guts, his ability to acept not only the blood that he shed in the first place (especially his family's

) but also the realization that it was evil all along, when such a realization would have driven me right over the edge....
And to top it all off, his capacity for love....to be able to love a new family after the tragedy of the first....
His grim determination to see the wrongs that were his life answered for.....his willingness to fight for an idea he couldn't possibly envision...
Sunder is the man!
Second favorite: Triock!
Triock was such a sad, bitter man....but he had even more strength of character than Atiaran, who was able to do what she had to despite the consequences to herself, but in the end was unable to handle it, and went mad....or Trell, whose despair (justified as it was, poor man

) led him in the end to harm the stone he loved....Triock was the one who held everyone else together for many years, he raised Elena singlehandedly, because everyone else was too messed up to raise a child....
And after it all fell down, Atiaran was dead, Elena was dead, Lena mad, Trell catatonic (he really is the King Lear here, danlo

)Triock still had enough love for the Land to find hope in the unbeliever, when he, perhaps more than anyone, had a right to wish him dead...
And in the end, to come to some kind of peace with him....
Triock and Sunder are very similar men, imho. Both strong beyond almost any other character in the chrons. Both able to face heinous wrongs, and not only survive them, but retain the ability to hope, and to love....
Least favorite would have to be Nassic, just because he had such a brief cameo in the story....although I love his story, another sad but hopeful tale....
Or Lena.....sweet as she was in the beginning, she just didn't have the guts that ALL of the others did. What happened to her was pitiable, and she did have guts.....her final scene in TPTP proves that....but there was just not as much depth of character there as there was in the others, imho.
Lena is the Ophelia of the Chrons....
As for who had the most influence, I'd have to say Lena though. As Covenant himself thinks in TWL, if she hadn't shown up, he might have died right there on KW, in madness and vertigo.....
And her rape had repricussions that lasted for 4000 years....