Okay so my first thing I would tell you to do is look up reviews and watch gameplay. That’s how I make my decision for all games I buy old and new. It really helps to see actual gameplay in a video.
My personal opinion is similar to others. I think sims 3 is great, but when I try to go back it’s hard. Sims 3 and 4 in my opinion are very different. I personally play way more 4, but it’s the current game and I honestly enjoy it more at the moment. I try to play 3 and I have a hard time. It’s slow, like it takes 10 minutes at least to load a save slow. I also have a very good rig and it doesn’t matter and it plays sims 4 like butter. Still takes forever to load 3, lags and stutters frequently with performance increasing mods. I do have all packs installed though because I can’t not. Yes sims 3 recommends on startup not playing with all expansions at once. It was/is that unstable. So performance wise it gets a huge thumbs down.
It is a great game though and I enjoyed it in its time. I never loved the graphics of the sims themselves. I have CC loaded in for the rare occasion when I do play it because I can’t take the way they look otherwise. The world graphics can be really nice though, i think it can be really beautiful. I prefer the style of sims 4, but that’s just me sims 3 isn’t bad looking just older. It does have a lot of fun content and I think any newer simmer who hasn’t dived in should. I do agree about waiting for a sale. The game will make you feel handicapped and it might not be your cup of tea, like I said very different from 4.