The Simpsons might be the 20th century Flintstones and Family Guy the 21th century Simpsons. Anyhoo, I like Family Guy better than The Simpsons (heneceforth FG and TS respectively) and here's why.
1. Relative Absence Of Irritating Voices
The voices of TS charachters are annoying all the time. FG voices can be annoying too, sure, but on the whole they're more agreeable. And the voice of Brian is spoken in Seth MacFarlane's normal speaking voice and that, my friends, is an artistic sign of moderation: "Go all the way, then step back" as Harley Earl put it. TS on their hand are overstating the comedy bit by making all the voices so "edgy" and "funny".
2. Slightly Anti-PC
TS are mainly PC scripts sprinkled with edgy jokes; to the core it isn't so satirical. Admittedly, FG is not a cutting-edge satire all the time but the anti-PC element is there. Like this dialogue with Peter sitting at home smoking crack. Lois asks him:
"What are you doing?"
"Where did you buy it?"
"From behind Black's hardware store. It was a white guy who sold it."
3. Tastier Colours
TS has gaudy, blaring colouring ("kids colours") whereas FG is more restrained in this sense, balancing pastels with rich, saturated tones (e. g. grey, pink and pistage along with bourbon, olive green and dark blue). TS after a while saw the aesthetical truth in this (more agreeable to the eye) and started to tint its colurs in the FG way.
4. Good Girl Art
Most TS women are ugly whereas FG can feature some "real hot chicks". It's not a porn show, I know, but it's the same syndrom as with the voices: TS has annoying voices and ugly chicks, FG has (in the framework of satire and all) almost normal voices and sweet looking birds too.
5. Brian And Stewie
FG has the characters Brian and Stewie, a drinking, talking dog and a machiavellian one-year old respectively. I know they say in the industry, "Avoid kids and animals" but FG:s Brian and Stewie are the exceptions that prove the rule. I won't even try to explain why these characters are funny. However, they enable a lot more stories to be spun around them than TS' more realist "silent dog and one-year old that hasn't learned to speak yet".
Coda: It goes without saying that FG copied the formula of TS, but other than that I don't care for TS anymore. It's the same with superheroes: DC invented them but then came Marvel in the 60's and took the concept to a wholly different level. Since then I regard Marvel as the golden standard of superhero comics and DC just can't compete.