Despite Celene's actions, find her better in the long run. Celene managed to turn a ruined Orlais into a powerhouse again because her predecessor nearly ruined Orlais BECAUSE of a war. Celene supports culture as shown by the University which a traditional ruler wouldn't have supported. Celene supports peace and in the long run would be more stable considering the endings where she is opposed are a result of her fighting Briala or Gaspard, not her own people. Her best endings make Orlais resurgent with culture and rights for elves if you reconcile her with Briala or if you execute Briala and Gaspard, Orlais prospers and soon goes back to how it used to be.
Gaspard on the other hand has no use for diplomacy. As far as he's concerned, force is the only way to do things. Very few people at the ball actually support him. Gaspard outright says he plans on invading Ferelden and he plans on killing people who oppose him as shown when he makes death threats to council members, his comment that things will calm down after some executions, and his ending where he kills people who oppose him. His ending outright says it's only a matter of time before a revolution occurs since killing anyone who disagrees with you can only work for so long.
If you support peace, choose Celene.