Generally depends on the kind of character I'm playing.
My ultimate romance (ideal) would be a male human rogue, a swashbuckler type, complete with sarcastic, witty commentary. No whining, no "talking about feelings" (at least not in the Carth/Alistair sense), and just generally gives you a reason to like him. Dark hair and eyes would be great, an olive to light brown complexion would be the best.
For a female romance, I've always wanted to see the leading female character be Asian or African in origin, complete with natural features, dark hair and eyes, if only to see something different than the standard Bioware female (dark haired Caucasian woman). If she was European I'd like to see a blonde haired/blue eyed (or red haired/green eyed) paladin or mage type. Only because Bioware mainly does dark haired females in terms of romance (Bastila, Miranda, Ashley, Jack, Morrigan) and it would be cool to see a lighter complexed female if she was Caucasian.
For male humans- male human warrior/rogue
For female humans- male human warrior/rogue OR female rogue/mage
For male elves- male elven rogue (Zevran)
For female elves- male elven warrior or mage
For male dwarves- female dwarven rogue
For female dwarves- male dwarven warrior
I like my male romance options to be strong or dexterous fighters, basically equipped for combat and not defenseless. I like my female romance options to be more persuasive and have some element of healing or magical ability, the exception being dwarves (who are not natural mages). Stereotypical I know but there's my answer