Calleigh did lose two people who meant a lot to her. As a character, she's been through some low points recently. But it says a lot about Emily Procter that she can do both light and cheerful and still pull off more serious scenes. (I don't think she's become robotic, but she was severely underused last season)
I guess it's just personal opinion, but Anna rarely lights up the screen for me the way Emily does.
Edit: I need to explain this further, before I offend anyone. (I know I'm swinging off topic here, and I apologise) Calleigh's robotic-ness, her generally low mood for the past season fits perfectly with what we know of her character and it's progression. Calleigh is the heart of the team - she lost two people. We've seen her go through mourning, although in CSI we don't normally acknowledge it as such. (Eric's lost his best friend, we'll have him act a bit weird for a while...) We don't know why Lindsay lost her temper a lot towards the end of NY season two, for example. And yes, it is a writing thing. Half of the time they don't seem to know who or what Lindsay IS, and we see her shifting and changing as the series goes on. So they want her on screen, but don't really tell us anything.
I don't normally like female characters. Maybe because I'm female myself, I find them two-dimensional and stereotyped a lot of the time. Calleigh, to me, is a wonderful example of a character written properly, a character I can like. She's feminine, yet strong, good at her job, and loyal to her friends. I love the fact she's a southern belle and a lady. We've seen her high and her lows, her mistakes and her weaknesses. Granted, she's been round a lot longer than Lindsay. But when Emily Procter acts, she lights up the screen. Off the top of my head, I'm thinking of scenes where she stares very intently at whoever she's talking to - Horatio, Speedle, Delko, Wolfe. She sizzles with all of them. It never needed to be said if she was flirting or that any dating was going on - there was chemistry and the fans picked up on it, which is why Calleigh is shipped with just about everyone. Emily flirts with us and the camera as much as Calleigh does with her co-workers. Calleigh fits Emily like a glove.
When I watch Lindsay and Danny, I don't get that same sizzle. I don't get the hairs standing up on the back of my neck, or the little laugh when I spot a shippy moment. Because I don't think Anna knows who Lindsey is, or how she'd react to a given situation. We need to see more of Lindsay as an individual, as a character with depth, before we can see her as a character in a relationship.
That's just my view. *shrug*