For some reason I've never been comfortable writing character sheets, I always seem to struggle to find the correct words to put in place. Consequently, I spend ridiculous amounts of time on a CS, I'm talking upwards of 4 hours for anything but the most basic of sheets. Dunno why, but even after years of trying I can't seem to pick up the pace. Having said that, it doesn't come as a surprise that I'm not a big fan of character sheets at all, however I can definitely see why they are necessary. 

In big groups they are kinda mandatory - you can't expect people to remember everything about 4, 5 or more characters, especially at the start of the story. In this case I'd like specific, concise details about the character - age, appearance (prefer written ones), defining traits, etc. Backstory is bit of a weird one. Sure, the GM needs it often enough, but as a player I don't really need to know where your character was born or what his first pet's name was, unless our characters know each other beforehand. That's something I may or may not discover during the story and, personally, I always enjoy learning something about a character that is not mentioned in their CS.

Also what [@NuttsnBolts] mentioned above is very spot on. Personality is hard to pin down, unless you've played the character before. Often I find myself writing one thing in the CS and then playing out a different character in the RP. Honestly, it's like trying to introduce a person you've never met. So I prefer having something like a bullet-list, which has basic personality traits such as "arrogant", "kind", "brave", etc. and you build up from there. 

In 1x1's I prefer not having any CS's at all, feels more organic to just discover these things over the course of the RP. I occasionally keep a small summary of the character on hand, but that's more as a frame of reference rather than a "true" CS.