For Federation, head to 17 Draconis, I was doing the rep missions before Horizons, and ranked up to Rank 9 in about 4 days of 2-3 hour stints. Plenty of missions to haul out of there after doing the Donation missions, about on par with Robigo runs, 20-30 million depending on your hold and about 10-11 deliveries back into the known galaxy.
**UPDATE** Still getting the Donation missions AFTER Horizons, hit Rank 10 in about an hour the other night. However the delivery missions are really strange, now the cargoes are huge for a so-so payout, and you can't take more than 3 or 4 missions and will be lucky to hit 12-15 million for a full cargo run back into the known galaxy. Brought my Anaconda out there to take some of the bigger payloads, but you can't hardly take any of the missions, because they require delivery to outpost where an Anaconda can't land.

Python is probably the best choice for a balance between payload and ability to land at outposts. Sadly I only have my trusty do-it-all Asp, and then went straight for the Anaconda, now it will be a long grind at these low rate missions to have the cash for a new Python.