Rommies can use 2 out 3 faction consoles. KDF can't use Rommy faction consoles.
BoPs have 1 less Boff slot, 1 less weapon slot, less shields, less hull. The uni lt com slot allows the tvaro flexibility to match most BoP builds as I mentioned before. The singularity abilities allow it hit and run more and better too.
The Rommy Cruisers are slower, but they have BC which when combined w/Rommy Boffs means more DPS. They also have singularity core abilities.
Fleet Mogai is a better version of the KDF vet ship b/c of console layout, and defensive specs (singularity core abilities).
Really power levels, carriers, and movement are all KDF have (movement only really noticeble at cruiser level), and Rommies can use plas leech and depending on ship/playstyle aux2batt.
Rom cruisers have a hard time using cannons, KDF cruisers can, that 15% boost for such a small time is not going to let them out DPS a KDF Battle Cruiser in the long run. Raptors are also slightly bulkier then most Tac ships and still have good turn rate along with it. I think it is more of an opinion then anything else, just like it supposed to be, some will prefer Romulans, others prefer KDFs, and others like Feds.