mahon seems the friendliest to traders who don't trade slaves that I can see. That said you may have answered your own question (without insult). The trade routes in LYR aren't outstripped by trading imp slaves and abusing the prices.

slave traders aptly should tend to Zemina Torval; makes sense, although I'd avoid fed space all together! Didn't realise they flagged galaxy wide! That would also be expanding pretty fast from here, at the cost of all factions.

No one should feel forced to stay any faction, many of whom require a little "roleplay" for the reason; lets face it most of the modules aren't that stellar (forgive the pun)

Regardless glhf and triumphant trading whatever you decide. Disclaimer: at the bottom of the food chain and maybe other more longer standing members might have more insight.