You might think of your step-daughter...
If she lives on the W side of Jax & the St. Johns River, then Herlong is more accessible than the others. If she lives over in the new bedroom communities S of Jax and W of the beach communities, Craig is very accessible...altho' it's a very busy reliever airport and ramp fees are probably a bit steep. If she lives well S of Jax, around the 9A/I95 Beltway, then St. Augustine is a lot closer than Flagler County.
If she's centrally located, I'd recommend Herlong. Recently refurbished FBO with the friendliest folks we've met at a public airport, the refurb was done around the traditional pool table that remains a fixture of the facility, new or nearly new hangars, and perhaps 5 mins from I-10 and so perhaps 15 mins from downtown Jax. Both skydiving and sail plane activity on the airport so keep your head on a swivel.
Paul, you may be wondering why someone would recommend visiting a bookstore (Chamblin's); what's so special about that? You really have to experience it to believe it. Faded, seedy-looking, smallish place from the outside...but plan on getting lost before you find all the aisles, back rooms and hidden treasures there. Take your old books with you, sell them at the entrance and then use the credit to buy 'new' ones.
Jack