A D1 please incl. the add on Hellfire, because it definitely expanded the game very well and the additional zones were very cool.
Otherwise, you can argue about whether you can upgrade it a bit and bring in comfort things like stackable potions and scrolls and more gold can be carried in a pile.
D1 otherwise has one of, if not the best atmos of the entire series, because in addition to gritty, they’ve also kept it more realistic and above all, through the wonderfully decelerated gameplay, conveyed the moment and thus the entire game much better.
And the fact that there is basically no endgame, but the game itself represents the endgame, is a real added bonus. Finally being detached from the end-game shenanigans keeps the focus absolutely on the game world.
If they would make it a bit bigger and deepen it, it would be the even much better Diablo game than D2 basically. Would only lack a little more talent development for all classes in detail, so that a warrior or the shooters and the monk from the add on would not only make autoattacks in physical combat flow and then also learn a few spells, but learn a few skills and these can also expand through these books that always drop for the spells or you can buy them.