IMHO the best system for Fed rank grind used to be Ceos/Sothis. That's very far out downsouth, but if you're serious about Fed rank grind, it's worth the travel. I finally went down there to grind for the FAS which requires a Fed rank of Chief Petty Officer, after endless visits to Tun and Taribes. The advantage of Ceos is that there is only one system (Sothis) nearby, so all the (data transfer) missions have a target in the next system and vice versa.
Therefore, you can do a convenient roundtrip, starting at New Dawn port, stacking as many data transfer missions as you can get (relog helps to get even more until the limit is reached which is about 20), then jump to Sothis Mining, sell everything you can there, collect new missions, fly to Newholm station, sell the rest, collect new missions for New Dawn, jump to Ceos and proceed as long as you wish. I would take only data transfer missions, as these require no cargo space. I managed to grind up from Petty Officer to Chief Petty officer in about 2-3 hours that way. At this stage, ranking up is extremely grindy IMHO, it takes 100+ missions for the next step. There also used to be rather lucrative long-haul missions if you're into making money, but I was into rank grinding first hand.
Now for the sad part, and that's why I would not go down to Ceos right now. The reason is that some geniuses recently UA bombed Ceos (by selling Unknown Artifacts to the New Dawn blackmarket, causing a lockdown) and are currently trying to bring down Sothis as well. Operations are underway to remedy this by bringing in meta-alloys, but currently it is not clear if and when this may succeed. It may well be worth watching the current state of the issue via the forums though, there might also be alternative systems you could go to, but currently, I know of none. HTH anyway [noob]