Which romance option intrigues me the most? Maybe Karlach or Minthara since the latter isn't implemented yet and thus we know the least about, the former because it has the least content in the game out of the available options and because it's seemingly exclusive to evil characters.

On the other end of the spectrum, Gale and Wyll, because of their Mizora/Mystra problems make it a 'complicated' relationship I don't care for.

Lae'zel and Asterion are near the middle. Lae'zel doesn't have much atm and is pretty casual, not really a romance. Asterion is a hammy vampire which has its appeal, even if he has 'bad idea' written all over him. Easiest to qualify too, since AFAIK it's only tied to how much he likes you, not triggering certain camp scenes or taking certain dialogue options etc. Shadowheart feels the most like an actual romance, which makes hers the best of the ones implemented so far IMO.

There's another option that's been datamined, but we don't know if it'll be in the full version and IMHO it would be better off if it didn't. I'll leave it at that.