Sims 3 is the only Sims game I have played and that I own at this time, but for me, I would have to say that I love building, creating and decorating the best at this time. I have made many changes throughout the town and to many of the homes. I have even built my very first home on an empty lot just today as a matter of fact. The only thing I haven't been able to figure out so far is how to make/build a basement. I have failed miserably at trying to learn to do that so far.
The one greatest lesson I have learned so far, and believe me I learned it the hard way, is that you should save your game often while playing. Save, save, save people, or it will eventually cost you a lot of time lost, much frustration, and lost progress in your game.
I read so much about WA on here. It must be a pretty good expansion pack. I would probably opt to play that one next, or maybe the new one that is coming out soon.