depends on what you are looking for.

If you don't mind the dated game design and structure, my favourites are 6, 5, and 4 these were the golden age FFs. You can get them as a collection in the Pixel Remasters. These games were way ahead of its time.

Then of course people are talking about 7, it's great but the graphics did not age well. It still plays well though, same goes for 9 (8 is a bit niche, I like it, some don't)

The feels changed drastically with 10 and 12 but they were great games in their own rights, 12 still feels relatively modern, especially with the remastered version.

Unless you are already a fan I'd skip 13 and 15, they are not bad, but they are not what I would want to point my friends to.

16 is also very different from the rest, being more action oriented than a traditional rpg, but the story is fire.

7 remake is not the same as 7, it's more like a sequel to 7 set in an alternate timeline so it's better to have played 7 first. Personally, 6 and 7 was peak FF for me.