I've got quite a bit of experience with the Marauders. The Oroshan are my favorite faction as an add on to other fleets and they offer a fairly straight forward play style. The RSN especially will be happy that the Oroshan have Fleet Tactics 3 also so there is no loss in Fleet Tactics.
The Armageddon is pretty stout with standard DR/CR but 11! HP and 2 shields
. Weapon Shielding as an add on makes their less then stellar AD values continue to dish out damage, despite any hits against it. The Turrets linking in against a single target also help boost those AD values up to something worthwhile and if you have a set of Griefs lined up with it there's a possible 23 AD to be had...
The Harbinger is also pretty good, though its SRS value is a bit low for a battlecarrier. It does make up for that with upgrades, but really I would focus more on this as a battleship with 5 wings. Weapon Shielding and +1 Shield are great and puts this on par with some of the best BB's around, once again the Griefs can boost their AD values up to something usable offering a decent 20 AD (ok 21 AD in a narrow 2" window linking the Turret and broadsides).
Defilers are
obscene They're fast, have squad size 4, great AD values in a full arc, good any arc torpedoes, above par armor, shields, high AP... They have simply jumped to the top of the medium landscape, easily one of the better medium options. Their downfall? Once you have taken Pack Hunters (Oh ya Pack Hunters... because 22AD frak ya!) these are 70 points, so ya... 280 points or 300 if you want High Energy too (great for boarding builds). You will have one of these, and not much else if anything for mediums.
Slayers also step up the game for their tier. There are not many Tier 3 options that I would call a must take, but if you're not bringing as many of these you can there's something wrong with your strategy. Their only real downfall is that those crazy four armed brutes are seriously too ready to board so you see AP 2 but only CP 1. 16 AD with Pack Hunters is good, really good, but 2x 10 AD attacks are usually better. These also work really well in smaller groups, but they do hemorrhage dun na na na Batlog points in smaller groups.
The Grief is back and forth with the Siren as best escort in the game imo. It has guns, but not just guns... lots of guns! Not to mention the PD or AP it can get, but I prefer to keep them cheap.
Omnidyne are very expensive and have Fleet Tactics 1 which ruins them in my opinion as an add on to any fleet other then Directorate (for which they're natural allies). I would steer well clear of these as allies for RSN mainly due to their abysmal FT value.
Corsairs would drop your Fleet Tactics also, but not as much. The do have a ton of options and are easily the fleet I have had the most fun just brainstorming ideas for fleets with. I don't think they would really bring much to the RSN though since they don't offer anything the RSN doesn't already do... and better.
Let me know if you any more input on anything and I'll try and put up some thoughts when I get on again.
