I like all of them, really. I had issues with Katie in S3, and I still do with Cook on occasion, but they're all great characters.

Character death isn't always a bad thing, if it's done well, for the right reasons, and not just for dramatic effect, and especially not just as a plot device. Chris's death 'worked'; it had meaning, and it was incredibly moving. It felt like part of a well thought out story line; and yes, it was devastating, but it didn't leave me thinking 'what the fuck? What are you even trying to do here?'
Freddie's death was completely random. It makes a mockery of everything that went before, and honestly, I truly believe it displays a contempt for the story, the characters and the audience. Sophia's death was bad enough (using a suicide to provide tension in a relationship? Yay, way to fucking go there, Jamie Brittain. Arsehole.) but Freddie's was just a whole other level of shoddy, lazy, contembtible writing. Random psycho on the stairs with the baseball bat? What are we supposed to take from that?
Jesus. I can't even begin to say how much this sucks.

(I've missed seeing you around, by the way. I hope all's good with you :))