The Sims 3
A friend of mine got an advanced copy and has been playing the Sims 3 for the past week. According to her, the game is not worth buying at this time.
The new interactions between neighbors, being able to walk around the town, and having your families continue to "live" even if you're not playing them, are very nice options.
Being able to add your own textures to furniture is just a simplified version of the object editor wizard that comes with SimPE.
She says that even with the vast details you can add to your Sims, such as how they behave and what they look like, they still managed to all look somewhat alike.
The most frustrating thing so far is that relationships take a lot longer to build. A couple that she started as soon as she got the game has had two children together but she can't get them to agree to get married after a week of trying.
And aside from all of that, it's still just the Sims 2, yet even more boring because it doesn't have all of the expansion pack activities.
So feel free to buy it and try it for yourselves, but if you mostly enjoy the custom content found on TSR and the expansion pack goodies, you may find yourself very bored, very quickly.