LogFAQs > #938593594

I'd recommend the VN since none of its animes really got the adaptation work right. Pretty long, though.
But from what you've already watched, I'd also say Zero (adapted from novel series), Ufotable's Unlimited Blade Works TV series (there's a DEEN Unlimited Blade Works movie, but it's super rushed, obviously), and then the Heaven's Feel movies.

Most of the rest are standalone side stories/spinoffs that you can probably jump into without a problem after some basic exposure with the franchise.

Lord El-Melloi II Case Files (novel, has anime) takes place after Zero and follows one of the surviving characters from that.
Strange Fake (novel), Prototype Fragments (novel), and Apocrypha (novel, has anime) are completely standalone.

As for the non-VN games, you have the Extra series that I think goes: Extra (PSP) > Extra CCC (PSP) > Extella (PS4, Vita, Switch) > Extella Link (PS4, Vita, Switch). There's also the Extra Last Encore anime series that uses the same setting and characters but is actually standalone.

The Grand Order phone game is standalone... I think. But it does have crossovers and references to other series from time to time. It's got some animes and upcoming movies for the more important in-game story arcs, but I haven't dabbled in them yet.

These are what I could remember off the top of my head, anyway. There are a ton of other stuff that I haven't tried yet.