Overall, the best romance scene went to Ashley in my opinion. The dialogue leading up to it was great, and I enjoyed getting to know who she was and what made her tick. The final scene, where she admits I make her feel good enough I found to be a bit of an ego boost. All I had to do was treat her like I treated the rest of my crew (like my teammates on a hockey team). The scene itself was what it needed to be.
Liara, I felt like she was throwing herself at me initially. That said, I was her first relationship (first and likely the best). They gave her an extended scene which I found to be a bonus. I like how they fleshed her out a bit more in ME2. FemSheps seem more suited for Liara than MaleSheps.
Kaidan threw himself at me even more so than Liara. And yes he did whine at times. One of my Sheps couldn't stand it and dumped him. Another one thought Kaidan was a sweetheart. So I guess it comes down to a point of view. And we see more of Kaidan than Ashley, which leaves me longing for a bit more Ashley sideboob even.
ME2 shows a wider variety of romance. Miranda's romance scene was a sexy display of power. She wanted everyone to know that Shepard was hers and put on a public display to do so. Jacob, Mordin, Tali, Kasumi, and anyone else who would have wanted to see that could have easily done so. Also, the buildup shows a side of Miranda who is either known for her looks or her setbacks. Finding the human side to a cold businesswoman is not something easily done. While she appreciates Shepard finding the human part of her, she also wants him to admire her looks.
Jacob gets a bad rap in my opinion. Talking to him on a friend level, he's straight up with you and doesn't mince words when getting his opinion across. As for the romance, the lines aren't the best. But one of my favourite moments was when he asked Shepard what was making her tick, and she can vent that she's lonely, or feels bad for the way things have gone. As for the romance scene... why he can be shirtless while Miranda isn't shirtless in the bed rest scene?
Those are the romances I've done so far. I've yet to experience the others for myself. But here's how I rank my experience.
T1) Ashley - Liked hers the best, and if we get a Virmire Survivor DLC to build on this, it could be the best. Otherwise it'll fall to #2.
T1) Liara - With her relationship fleshed out with the Lair of the Shadowbroker DLC, I became a bigger fan of her. Even as a friend, I like the scene on the Normandy where you get to speak with Liara one on one.
3) Miranda - Bit divided on this one. I thought the process of the Jacob romance was better, but Miranda's did have better dialogue. It showed two sides to Miranda's personality (her business side and her human side) and this culminated in the engine room.
4) Jacob - The fact he's to the point and not wishy washy is good in my books. Just wish he wasn't monotone at times. His lines are also very questionable at times and I have concerns about him seeing Shepard as simply a sex object. Hopefully I'm wrong.
5) Kaidan - Some could interpret Kaidan as sweet, others a whiner. But the way he's throwing himself at you leaves me shaking my head.
I haven't ranked the others, but I look forward to playing out the remaining romances and then ranking them.