About Halo Reach:
I'm a bit torn on each Noble's death. Jorge, Carter and Kat's were pretty sad IMO. 6's was meh. I hated how Emile's was framed. Seriously, the guy went out like the bada** he was and yet we barely saw it.
However, if we're talking about AI companion deaths in squad-based shooters,
Star Wars Republic Commando blows Halo Reach way out of the water (and I love Reach). Sev's death in RC hits much harder IMO.
That's probably because Republic Commando does such a good job of making your squadmates feel real. Noble Team looks awesome, but most of the time they just got in the way. In RC, you really get to know, care for and rely on your fellow clones, especially Sev (for some reason he always seemed to have the most lines and be the defacto guy for doing the slicing/demo/sniping).
As much as I didn't enjoy that final mission and the ending cinematic, and even though I'd known about Sev's fate for years before playing the game, it still hurt.