Personally, The Sims 1 always holds a special place in my heart :)
Between these two though.. Hmm.. I personally believe The Sims 3 to be the better game here.
Reasons:
The Sims 3 is the most up to date/current game.
Always being updated
Expansions are coming out (Latest being "Late Night" which is AWESOME!)
Much better graphics
The Sims are easier to manage (don't always need the bathroom or food.. Leaving you to do the fun stuff :D)
Exploration of the whole town.. Feel like going to the store? In The Sims 2.. This requires a load screen as most things do.. Yet in The Sims 3 you can just walk/jog/run/drive straight there in no time :D
Also I don't believe you can get The Sims 2 now on a legal digital download.. Yet The Sims 3 and it's Expansions are available here:
http://eastore.ea.com/store/eaemea/en_GB/ContentTheme/pbPage.sims3uk
However The Sims 2 though is still an amazing game.. But I'm still going to have to say that 3 is the better game :)