Don't hate her, and I always go random so I never choose against her, but if you forced me to pick my least favourite character she'd win out of both games.
I've yet to play through either game fully on single player, preferring to play with friends and avoid horrendous bot AI, so all my experiences are pretty superficial based on mainly thier appearance and the bits of catch phrases you hear when noone happens to be talking on ventrillo.
From L4D, I loved Bill and Francis from the very first cutscene. Thier interaction throughout the game, and just thier imagery was both obvious enough to understand and humerous to like - Francis is obviously Biker/Tough Guy and Bill is obviously the guy with his head screwed on that kept the survivors alive.
Louis and Zoey I liked less, but still accepted as they were clearly defined relatable characters. Louis reacts alot like you'd expect Joe Bloggs office worker would given the Zombie Apocalypse. Again, his character model reflects this. Zoey, dressed like some Uni student and references pop-culture so again, whilst "the girl" is still relatable, if not one of my immediate favourites.
L4D2 sucked me in with it's cinematic. Ellis won my heart through that alone, which was only furthered by the game. Nick if possibly my favourite with his "wit" and comments, and Coach is great. L4D2 goes all-out stereotypes, Hillbilly looks like one from a mile away, Highschool Football coach looks like one, and dubious gambler looks like he fell right out the 80s cliche machine. Awesome.
So when I first saw Rochelle (hell even her name screams it) my first impression was she was trailer trash which set me against her - and her cocky attitude pissed me off when combined with my impression of "Trailer Trash" (like chav's piss me off in real life - What do you have any reason to be cocky about?). I was massively suprised when someone pointed out to me she was actually meant to be a reporter. NOTHING about her screams out that she's a reporter.
Which says it all really about her character design. All 7 other characters you could show someone who hadn't played the game before and ask them which Movie/Game Stereotype they filled and they would answer correctly (be it biker, student, hillbilly and so on). Show someone a picture of Rochelle and I bet noone would guess "Spunky Action Reporter". Which is a failure of character design, and a reason why so many people can't relate to her - mixed messages as to which cliche they are meant to be relating to.