For me, if it's only between those two, I would stick with s2. In fact, I have reinstalled it recently and I've been playing some of it last week alongside the others.
And even as a base game (which I had a long time until Nightlife, but even then, my sims didn't go downtown or use cars much, etc), TS2 was and still is better than ts4. Ts4 feels like an imitator with better graphics. Ts2 has more polished life stages, rotational play, more detailed animation (and more mature make out sessions, lol), more sandbox and better AI that actually reacts to events. Ts2 wishes actually make sense and are adjusted according to personality, aspiration, and any major life changing events.