ETA: MAJOR MAJOR MAJOR SPOILERS only read if you're caught up
Favorite characters: Tyrion (like everyone else,) Sansa, Jon, Varys (especially after he reveals his goal the whole time had been to get the Targaryens back on the throne-he's like the ultimate puppetmaster,) Renley (RIP awesome gay dude,) the Hound, Melisandre (she is just super weird and awesome with her fire cult and giving birth to shadows and red eyes.)
Least favorite characters: Cersei (her getting POV chapters granted her no depth,) Theon (even when Roose broke him mentally I couldn't feel too bad for him,) Arya (she's like a junior sociopath,) Catelyn and Bran (neither does nothing interesting,) Arianne (her chapters are SUPER boring,) anyone involved in the stupid Iron Islands plot that I do not care about at all.
Best character development: Jaime by far, becoming a totally different person.
Worst character development: Probably Cersei, who doesn't change at all pretty much, even after being paraded through the streets bald and naked.
Best plot events: Tyrion killing Tywin with a crossbow after years of verbal abuse, the Red Wedding (for the sheer crazy factor,) that bizarre scene with Daenerys in the House of the Undying, Viserys having molten gold poured on him (never gets old,) the insane discovery that Aegon Targaryen is still alive and has been hidden in Essos by Targaryen loyalists.
Worst plot events: Bran and the three eyed raven who turns out to be some magic Targaryen, which is just weird and pointless, anything involving Samwell p*ssing himself, the porno scenes between Jon and Ygritte, anything to do with the Iron Islands or Arianne and House Martell, Catelyn turning into some weird revenge zombie.