Strongly negative —
谄媚 always implies insincere, self-serving flattery aimed at someone with power. Compare
奉承 ("to flatter", more neutral, sometimes even social-lubricant),
拍马屁 ("to suck up," colloquial and vivid),
讨好 ("to ingratiate oneself," mid-register). Of these,
谄媚 is the most literary and the most damning.
