I never romanced any of the female LI's. As a straight female myself, I'm only interested in the male romances.
The Iron Bull romance is very nice. I love how sweet and affectionate he can be to the Quizzie, and the game makes it clear that he's very careful to do things that he knows she likes and enjoys; he never pushes past what she's comfortable with. That being said, I did find it a little difficult to be in what seems to be a completely BDSM relationship. I enjoy some tie-me-up-tie-you-down stuff myself, but being in a relationship that consists only of that makes me slightly uncomfortable. I was able to headcanon that aspect of the relationship as being on the mild side during the main game, but in Trespasser when they made those comments about shackles and doing it while the Quizzie was hanging from the chandelier... I wasn't too crazy about that. That being said, Bull is very attentive and supportive during the romance once you get him to that point. It's clear that he loves the Quizzie very much, and that makes it easier for me to play through that part.
Blackwall is also a sweet romance. He can come off as being self-pitying to some people, but I see it more as him struggling with "How can I love such a wonderful person, and even worse, how can I allow her to continue to love a murderer?" It's a struggle where he wants her, but can't come to terms with someone as amazing as her loving someone who has done things as horrible as he has. He's very loyal and supportive, though, and I love how he loosens up and jokes around once he's been accepted for who he really is.
Cullen is a fantastic romance as well, I think. I'm so glad they added him in, and for being a late addition, they did a great job with him. My own personal recommendation- romance him as a mage, and also have your Warden be a female mage too. It adds this new dynamic to the romance that I don't think you get otherwise (though of course the romance is great either way). I know its a bit sappy, but I love the "happily ever after" ending where you get married and see his family. I think it's sweet.
Solas... Solas is okay. I wasn't crazy about him, and I was sad at how his relationship with the Quizzie ended. Maybe if you romanced him and decided to redeem him in Trespasser, their love will have a happier ending in the next game. If you like angst, though, have at it.