I don't think I need to dwell on why Haley is better than Trump. Here's why she's superior to DeSantis (the only other candidate with even a remote chance):
She supports cutting entitlement spending - the only possible path to heading off the awful fiscal crisis coming our way. Indeed, she's the only significant candidate in either party willing to take this position.
She supports aid to Ukraine. DeSantis waffles on this, and Trump is even worse.
Unlike DeSantis, she has no record of attacking freedom of speech ("don't say gay" law, using government power to persecute corporations that speak out against his policies, etc.).
Likely to be better on trade.
Somewhat less bad on abortion (DeSantis signed a 6 week law; Haley has advocated less extreme measures than that).
When she says something stupid, she usually takes it back quickly (e.g. - Civil War comments, proposal to ban anonymous posting on social media). DeSantis and Trump almost always double down on their evil and stupid ideas.
She doesn't promote anti-vaxxerism. DeSantis does.