KDF - Only because of Gorn's. Cause Gorn's are cool.
FED - Cause Excelsior's are cool and they have kitty's flying them.
If Romulan's had a alien Furry ( or Anthropomorphic if you want to get all techy and all, and I know you will dear reader ) like race or what ever their called, I dunno.......Alurrys.....main thing is that I'd play it.
The Klingons attacked and invaded the Romulan Star Empire in the backstory. Although the Republic is a different entity, it's still made up of Romulans, and the antipathy that exists between them and the Klingons is way more excessive than the antipathy that exists between Romulans and the Federation. Plus there's the reunification movement to consider, and that weighs it more towards the Federation.
If I were playing a Reman though, I might lean more towards KDF.
Both, depending on character goals and the personalities I've tried to play the different captains with. Generally, Fed-roms have easier access to fleet stuff (since Fed fleets are usually further along) and cheaper doffs and special equipment, plus faction-specific queus pop faster due to the larger Fed population. KDF-roms have better doffing rewards though, and better consoles to pull from other cstore ships.
It won't affect your story though. You're still a member of the Romulan Republic doing Romulan missions, requesting aid but not selling your soul. Pick the side that serves your ends best, as any true Romulan would.
My decision as based on how romulan ships are built. Since the singularity core gives us lower overall power levels i chose klingons. I bought the Vandal Destroyer which has the plasmonic leech console. So now pretty much any of my Rom-KDF toons, even my regular KDF toons can claim the ship and take the console to help buff my overall power levels in combat.
KDF, because I can get Elite Disruptors, and because I paid ten bucks for a Vandal years ago and it may as well save me some EC now. Also the costume options are much nicer. And in conclusion, Sugihara is an annoying idiot.
I did align one Rom with the Feds, but I haven't bothered leveling that character up much.
I am allied with the Orion Syndicate and the Klingon Empire.
There are numerous reasons for this choice, not least of which was the overbearing snobbery and prejudice of the Vulcan ambassador in the mission where we talk to Feds and Klingons before the bomb goes off that changes the tune of both the UFP and Klingon Empire.
Also, I cannot fly a D7 if I ally with the UFP, and that would suck majorly, since the only female Romulan seen in TOS was commanding a squadron of D7s.
And female Orion allies are helpful to a character who lives for espionage (my character, the head of the Tal'Diann).
Plus, Reunification is not a bad idea, but it will not happen until the Vulcans realize they messed up, and that doesn't seem likely any time soon.
So, until then, I'll just keep seducing individual Vulcans to march beneath the Raptor's Wings, and blasting away at Starfleet vessels in places where they shouldn't be.
Which Faction did you choose, why, and how do you like your choice?
My first rom joined the federation, for two reasons. 1 because cryptic suck balls and wont allow romulans to be their own faction(RUDE surprise btw after all the 'march beneath the raptors wings hype) and 2 what the RR needs is infrastructure and the UFP is better in that department.
My second rom did KDF for three reasons the first is the same as my previous character, the second is that their uniform is cooler, the third he's conspiring with his sister to overthrow D'Tan and his reckless unificationists and admirals that would risk Mol'Rihan by activating an Iconian gate that has already devastated the planet once. For that they need military power, and war is what the Klingons are good at