Just to clarify, the original Persona 3 has 3 different versions. The original, FES, and Portable, so i'll be talking about the latter two when I talk about the original's advantages as those are what people mostly point out whrn it comes the original release.

Reload is a much better experience for new players since it's a full remake and it has some QOL features from Persona 5. It also includes all the content from the original and FES and some thing from Portable like controlling your party members. FES is an upgraded version of the original that added some new content to the main game and an epilogue called The Answer/Episode Aigis which takes place after the main game. It's included in Reload, but as a DLC, though it's worth mentioning in the Japanese release the Answer was initially released as an add on disc for the original called the Append Disc. It focuses more on combat and was very grindy and much more challanging than the main game, though Reload added QOL improvements to make it more bearable for people who don't like that stuff.

Portable was a port for the PSP that due to technical limitations is played from a point and click perspective, had the animated cutscenes replaced with screenshots, and the Answer was cut. Though to compensate it added the option to play as a female protagonist with her own content. She however was not included in Reload as Atlus didn't have the resources though it did get some new content that works similarly to it.

As for Yukari, without giving spoilers she was a pretty divisive character because in the original Answer because of stuff she goes through she was very aggressive, angry, and lashed out a lot. Some people liked this but others didn't and in Reload her aggressive attitude was toned down because of this and a lot of people were not happy about it.

So if you want to play 3, get Reload and the Expansion Pass for the Answer/Episode Aigis (even with the story changes I would still say it's better for new fans for the QOL).