Kaidan was sort of a tricky case for me. My first playthrough I was a Male Vanguard who always had Tali in my team. So Kaidan didn't get used because he brought nothing to the team that wasn't already there. (Already had a techy, a biotic and his weapon/armor were poor).
My third slot usually defaulted to a Ashley, Wrex, or someone I thought would be good for a particular segment. He was so horribly underused that when Virmire came up, it was no contest who'd I try to save. That's when Kaidan had what I felt was his shining moment to me. A spectacular and moving death scene.
I mean this honestly, not jokingly. Here is this guy I never used and I felt truly horrible about what happened to him. Was an emotional moment. Because he died so well, I decided I didn't give him nearly enough of a chance. So when I did my second playthrough as FemShep, I decided he earned his chance in the sun. I planned not only to use him as much as Tali, but make him the Love Interest as well.
This was where my problems with the character came in. He was so very wish-washy in the relationship, and so very unwilling to commit to actually saying he wanted to be in one, that FemShep started feeling she was Sexually harassing him. The only time he showed any interest was when he started giving her crap about Liara (Which happened before I ever actually had a private conversation with her). The relationship started feeling increasingly unsatisfying to me because of how he wouldn't step up to it.
So that's the story of the lower rating Kaidan got with me. Nice guy but not useful to me on Maleshep, Highly annoying as Femshep. I thought it might have just been me until I heard my wife screaming about Kaidan on her Playthrough. She was begging for a Renegade Interrupt on Horizon when she ran into him.

Jacob got a more 'mediocre' score with me. Thought he was a great guy and very useful on either playthrough, but as the game went on you get much better squadmate choices. As Femshep, I found talking to him extremely awkward, mainly due to FemShep's lines. So that cost him some points.