I don't believe the assassin (what's his name again?) would have
done it to anyone else. He just hated Garfield for being too
reformist-minded and didn't give him a job offer.
Grant, Sherman, Blaine, or any Republican would have won the 1880
election because Hayes did a decent job for the next Republican to
finish his second term for him.
Regarding the VP, none of the names you mentioned would have taken
the choice (Arthur) of the bully Conkling. But Garfield, being the
more obscure figure, lacked the power to say no.
Who knows what these other guys would have chosen, only losers
wanted to be the Veep back then.