Ouf, tough decision, I don't think I can actually pick one of both!
I love how detailed I can create my Sims in Sims 3 and they are all different! It just depends a lot if you take the time for it and maybe it needs some practice or something. I also love building in the Sims 3. However in gameplay I think Sims 2 wins. Eventhough Sims 3 has so much I'm not even close to having done everything. The family play in Sims 2 is just better for me. I love both. The only thing I just can't love (yes I have tried) is the Sims 4. Speaking of pudding faces... and that awful neighbourhood overview! Or the lack of cars (in which Sims 2 wins btw, Sims even getting in their car and all!)
I wish for a Sims 5 with Sims 2 family play, cars and lots, Sims 3 CASt, skills, CAW and open world, Sims 4 parts of building mode and parts of CAS and then realistic graphics like any other game.
And honestly I don't care much for the LHBT+ add on in Sims 4, I liked that there was just one type of Sim we all had to adjust to. I'm an autistic, religious simmer and I don't have any special options... neither have crippled fans or fans with OCD or deaf fans. Why the exception for LHBT+? To me it feels a bit like all or nothing...