I started with TS3--as back then, it was enjoying good discounts on Steam, while TS4 was not (even on Origin, which I had for SimCity 4 and a couple other games). The only problem I have is that it's very intensive, and being 32 Bit, it doesn't really work that well on my PC, since it can only use like 2GB of that. I have a consumer-grade PC with a really good i7 for the period TS3 was current (third generation), and 16GB of RAM. With that amount of RAM, and being able to use as little as half of it, I am sure the game would be just a tad more stable, and quit crashing. Or, get off my rear end and finally get around to building that gaming PC.
It's a much better game. I had base game from 2018 until late, late last year. The game was full of stuff to see and do, and most of the world was interactive, and you could visit most places in the game, including landmarks. And this was just base game without all the (very excellent packs. Vs. all the decorative fluff, fewer lots. I will say this--TS4 still has the better-looking Sims, and easy to use CAS. I can only get ugly and really ugly Sims in TS3.