moxie is good because salamence gets an extra attack boost when KO-ing a pokemon. i also did not choose intimidate because if the opponent is a special attacker its useless.
Definitely go with moxie because it raises your attack upon KOing a Pokemon. Intimidate is practically next to useless now because 1) they can just switch 2) It only works as soon as you get/switch in.
Moxie is the best choice. Salamence is strong enough to hold out against most attacks, and can deal out some heavy blows to KO a Pokemon. Intimidate doesn't give the full benefit to Salamence as Moxie does.
hope this helps =)