I prefer Sims 3 because I hate the fact that you have to 'unlock' stuff by going through careers and I'm too easily distracted to get someone all the way through several careers in order to unlock everything.
Also, this is hugely nitpicky, but I hate how there's no way to stop sim kids and teens from having to go to school. I like making my own schools and playing it out, or are just too interested in what the teens especially are doing to shove them into a place I can't see them for sim hours. I have enough of school in real life!