I saved Kaidan, because I really can't stand people like Ashley. At least the headachey, obsolete, depressed biotic guy wasn't a damn xenophobic zealot.
Plus, biotic companions tend to be more useful than shooty companions in my experience. I can handle the required shooting, while biotics are a pain in the ass to hit anything with... so I make the AI handle that on my command (honestly, my companion loadout of choice is one pure biotic, one Vanguard... so human companions tend to get no love).
My recommendation: save the one who shoulders headaches rather than causing them.
Plus, biotic companions tend to be more useful than shooty companions in my experience. I can handle the required shooting, while biotics are a pain in the ass to hit anything with... so I make the AI handle that on my command (honestly, my companion loadout of choice is one pure biotic, one Vanguard... so human companions tend to get no love).
My recommendation: save the one who shoulders headaches rather than causing them.