2 or 3 depends on personal preference really, even fully upgraded i think 2 did some things better then 3 that puts it above for me, and even though 4 was designed to be a "Laptop Game" i would still put 1 on my laptop/toaster before it.
2 has no less memory leaks and and Turn-Ons/Turn-Offs were a great addition for Create-A-Sim (you can basically decide sexual preference immediately, bypassing that RNG shit.) and it built naturally on the lore of the first one while 3 kinda went "FUCK YOU" by being in the past AND the future at the same time, and i ain't talking bout the last expansion.
It basically had the most interesting Neighborhoods, but you have to juggle families since time stands still for anyone you are not playing, and doing so basically resets your wants, so many feel discouraged but the static state of the neighbors can be a plus for some people.
3 got KW though which is pretty fun if you get it working, though more for humor then actual fap material and the "Open World" is more trouble then it is worth for a good amount of it, especially sicne you do still need to switch "Open World" fucking constantly if you gonna do expansion gimmicks anyway. No, thge REL feature that makes Sims 3 competitive is Create-A-Style, which is the reason for much of the Memory leak, traits are good but ultimately ended up having a shitload of "dud" ones due the expansion specific shit, resulting in situations like Sims having Island Paradise related shit when playing on a map that doesn't have them, it also kinda suffered with having too many "Townies"/Randomly Generated Hobo NPCs, part of the fun is the neighborhood, and despite the openworld, and in the case of some BECAUSE of the openworld, it was hard to get to know the neighborhoods since 90% of the time what you would interact with would be a Townie and even "neighbors" could live far away, so you never had "Oh, My neighbor is having my other neighbor over" situation. Basically, the story progression sucks.
4 is basically 1.5 in theory, even though i remember it being "ALL ABOUT THE SIMS!" this time around, the CAS is stupidly limited, not only in clothes (due MICROPAY GOY) but also in way to give your sim personality and goals, and it i s by FAR the most dry one vanilla, yes, dryer then Vanilla 1, Get to Work at least added somethings to do and Get Together is basically a glorified cheat due groups being too fucking good due the brainwashing rewards basically letting you ignore the fucking core mechanic the rest of the game works off, base game tried to hard to be quirky(LE GOOFY WALK) and the expansions, though attempting show no sign of fixing that, oh, and despite all the whole "Dongrade so it can run on laptos" shit they STILL had memory leaks and shit, so it is worse then the 14 year older predecessor in every way aside from the fact Sims age, basically ==DO NOT BUY!== and that is before the "LET'S BREAK THE GAME TO BE PROGRESSIVE" patch.
1 kinda does becomes a wreck if you have all expansions, not due memory leaks unlike 3 and 4 ,If there are any they are irrelevant due technological progression, i know i thought it was slow as molasses if you had it all installed as a kid though, but hard to say how much of that was due playing on a toaster and what not), but because there are too many features which makes shit into a cluster fuck and some of them have questionable mechanics.(IIRC Vacations were clunky to do and often detrimental to EVERYTHING.), Unleased is to this day what i consider the most gamechanging expansion (And probably the reason why Fans wanted "Pets" for 2 and 3, so badly not the pets themselves, but because the association of the huge QoL upgrades the expansion brought alongside them, though i think 3 Pets snapped em out of it)
1 kinda does have issues due the GRAFIX but also some good shit, i like em and i think there are "HD mods" that keep the visuals acceptable, but the GRAFIX do result in the "Head/Clothes" CAS system, which can result in samey sims, on the other hand, sims will usually dress like normal people unless thy just got "THAT" outfit and most outfits did hit "Soap Opera" cliches that made archetypal assumptions easy like Bella Goth being eyecandy in the Little Red Dress, and the advantage is it is piss easy to make your own content, just open paint and get to it, and that is piss easy "modding" even by piss easy "modding" standards, the point system was interesting but players tended to extremes or "perfectly average robot" so i can see why it was scrapped.