I hate how useless Krillin, Tien, and Yamcha became in Z. They were literally there just to be killed off all the time.
Yamcha and Tien were never really Goku rivals though. They both only beat Goku through luck (Goku was hungry against Yamcha, the car hit Goku in the tournament). At least Toriyama gave them something to do in the Cell arc. Yamcha finds the Androids and discover their ability to absorb Ki, Tien briefly stalls Cell to allow #18 to escape.
Krillin wasn't too useless in Z. He did best against Nappa then any non-Goku character, and he helped beat Vegeta. He saved Vegeta's life on Namek (who in return helped Goku beat the GInyu Force once Goku's body was stolen). He doesn't do much in the Cell arc, but he still gets the storyline about the whole #18 thing. See below for Buu arc.
Refresh my memory, what did Krillin do during the Buu saga? I haven't watched it in ages.
Grew hair, and fought some dude at a tournament. At that point Mr. Satan had replaced him as the token human.
Goku, Vegeta,Gohan, and Krillin got all the Hot chicks. Yamacha is the only one hating.
Yamcha technically tapped Bulma before Vegeta, also he had another girlfriend in the Cell arc.
I find it funny that Future Trunks (who is going off Bulma's side of the story) says that Yamcha cheated on Bulma and left her. But when Baby Trunks shows up, Yamcha complains that its actually Vegeta's kid, implying Bulma left him.
Yamcha has no highlights.
He and Puar defeated Oozaru Goku, and beat Invisible Man thanks to his girlfriends talent.