If you've never done romances before, I'd suggest starting with one of the official ones. All have individual strengths. Aerie is innocent but has a bit of a tragic caste. If this isn't your cup of tea, she'll annoy you quickly. If you chose Aerie, I would recommend picking up Haer-Daelis. It does spice things up a bit. For that matter, the Keto mod complexifies this love triangle even more. From my experience, Aerie's is the most interesting ToB relationship. It's decent in SoA, and probably one of the strongest if you like her character and bring Haer-Daelis along.
Jaheira's is the most involved in SoA. Quite frankly, though, it's the weakest in ToB (at least that was my impression). Her personality is more aggressive and controlling than Aerie. The romance evolves out of your prior friendship with her and her husband. Again, if you enjoy romances that grow out of comraderie, hers will be appealing. I've never liked her personality as much as others, but it is an entertaining and complex SoA romance.
Viconia's is both the most "fun" and the most unhealthy relationship. You get to be a bit more forward and even insulting with her. It can be entertaining in places. It's most ideal for evil characters, though it will work with a ranger. You can actually 'convert' her, sort of, I believe. So that may be a goal to shoot for. In ToB it stays on course. It's stronger than Jaheira's in ToB, probably.
Whichever you chose, I'd encourage you to download the Flirt Pack (and probably Banter Pack as well) from the
Pocket Plane Planet. It adds a bit of color to the romances.