I don't hate any of the protagonists, but I of course have my least favorites.
* CJ - I used to think this guy was just the coolest when I first played the game, but over time, yeah, he's a bit of a whiner. I can see what Rockstar were trying to do, by having the protagonist be an ordinary guy (more or less) thrown into this crazy situation, but it doesn't make for the most engaging protagonist for this kind of game, and overall he's rather bland compared to the much more interesting Sweet. I actually think Sweet would have been a much cooler protagonist, really. Thinking about it, if they'd been able to introduce the multiple protagonists feature back then, it'd actually be kind of cool if the initial Los Santos portion had you playing as CJ, but then instead of CJ being forced to do Tenpenny's dirty work and Sweet going to jail, it'd be the other way around, and you'd find yourself playing as Sweet for most of the remainder of the game. He could do pretty much all of the stuff CJ wound up doing, but with the carrot on the stick of not only freeing the only brother he has left from prison, but building up an empire around SA and becoming powerful enough to retake Grove Street. But I digress.
* Luis - He's okay I guess, but easily the weak link of the IV trio. I found him pretty bland for the most part, kind of like a proto-Franklin, but at least Franklin was in a somewhat more interesting situation and was pretty funny as the "straight man" in these crazy adventures. That said, I love his relationship with Tony. It's the heart of the game, and they make an engaging duo.
* Trevor - Hoo boy, I don't think I've ever felt so conflicted about a protagonist. Let's get the bad out of the way first: He hams it up WAAAAAAAAAY too much and is inconsistent as hell writing-wise. It's like they wanted to have their cake and eat it to by having this deranged, bloodthirsty psycho as a protagonist, but at the same time have him be this wacky, funny, and sometimes sympathetic nutcase you can laugh at without feeling TOO unnerved by. And while his story with Michael is pretty engaging, his own story (building up his empire in Blaine County, his scuffles with the Lost, Aztecas and Chinese, the godawful "romance" with Patricia Madrazo) feels out of place and interferes with what IMO should have been the central story, the relationship between Michael and Franklin. But on the other hand, Steven Ogg's performance is outstanding (even with the aforementioned hamming it up), and there are a couple moments where the character really shines. Like in the controversial "Mr. Philips", or most of "By the Book" (despite that OOC "Torture Advocate" speech at the end that was less Trevor speaking and more Rockstar on their soapbox), or the opening cutscene of "Fresh Meat", he really comes across as this horrifying, disturbed monster of a man you feel uncomfortable playing as, and I mean that in a positive way. I also really like the moments showing he's a lot smarter than he looks, like his assessment of the docks in "Scouting the Port" (one of the few moments I like in an otherwise yawn-a-minute snoreathon of a mission) and not falling for the mostly fake coke in "Hood Safari". A violent, unpredictable psycho who's dangerously intelligent; that's the Trevor I wish we got. Rather than the Trevor we did get, who's that as well as this weird, funny, crazy uncle who cross-dresses, pisses and sh*ts in public, blubbers while driving the woman he kidnapped and fell in love with back to her husband while listening to Chicago, and asks people to marry him before killing them (really... WTF?!). Overall, I will say that I like the character overall for those aforementioned flashes of greatness, but much like the rest of GTA V, he could have been so much better.