Hina’s the clear front runner, but don’t count Tsuru out...she literally washed some dudes out of commission at the Battle of Marineford, had been chasing Doflamingo for quite a while, and was evidently close with Garp and Sengoku back in the day. If nothing else, she’s probably got some stories to tell in a narrative sense.
Also, not for nothing, but it’s pretty telling that Oda has introduced dozens (maybe hundreds) of Marines through the course of this decades-long story, and only 5 or 6 of them are females...even then, we’ve really only seen one get much character development, mainly in the service of a main male character’s ultimate goal. I know his writing usually leaves little to be desired, but that’s one clear area in which he lacks.