I have to take Mark Lenard's original character (who is called Keras in some ficton and was my avatar for a LONG time) out of the running since Mark basically originated the standard Romulan with that role and it's hard to stack anyone up to the original.
As far as developed Romulan characters, I'd say Carolyn Seymour's Toreth and John Fleck's Koval were the best of the contemporary Romulans.
Honorable non-fully fleshed out mentions to Tal (of course), Martha Hackett's T'Rul and Adrienne Barbeau's more interesting version of Cretak (IMHO).

As far as developed Romulan characters, I'd say Carolyn Seymour's Toreth and John Fleck's Koval were the best of the contemporary Romulans.
Honorable non-fully fleshed out mentions to Tal (of course), Martha Hackett's T'Rul and Adrienne Barbeau's more interesting version of Cretak (IMHO).
