DS9 and surrounding sectors are good for trade.
As well as recruitment, it offers the option to take Cardassian dissendents in Asylum as well as Paradan & Karemma Officer Exchanges. Just fly between the sectors in that region.
Might need to have some chains done.
At least, when I still played. And yeah, recruitment is the only one I hadn't maxed, as the Academy ones don't work so well when you only have 100 Doff slots.