Kaidan's story is actually somewhat intriguing, unfortunately, they made his character as bland and uninspiring as possible. He should have been real jittery, having short bouts of anger similar to Terret's(SP) syndrome... this, of course, being a complication with his L2 implant. Give him a wacky bedhead haircut coupled with bloodshot eyes that are constantly wide open, and Kaidan would easily be my favorite character.
Getting back on topic, I always seem to pick Ashley. Maybe because... I don't know... she's actually useful compared to Kaidan.
You actually belive Ashley was more useful than Kaiden? lol. Soldiers are only good when your that class. Kaiden had much more useful abilities than ash. But yeah, I played the game three times and kept kaiden alive twice. First time through I romanced liara and choose kaiden because that reject killed wrex. Then I choose Kaiden again because I romanced him. I only kept ash alieve on the story where I romanced her.
If you need biotics, you've got Liara, even Wrex. Kaidan might be useful for some tech , but that's easy to get around. I don't know about you, but it's not very helpful to me when Kaidan dies in the first 5-15 seconds of every conflict. And I play with a team mindset, despite the fact that it's all AI.
Ashley is just a tank that is good for laying down constant firepower. She's reliable and never dies. I forgot that I even had the unity skill at times, but Kaidan quickly reminded me... over and over again.
I play a very balanced team. My most effective team thus far has been my AR adept with Ashley and Tali. Balanced combat, biotics and tech. This team has made insanity feel like normal difficulty.