Echo all these. The Europe '72 was what first got me kind of more interested when I had dismissed them in high school/most of college and was way more into Phish until my 30s.
I found myself watching The Grateful Dead Movie the other week thinking that it would be a good intro for people. I feel like they have some of their more famous songs there, they don't go too far out, but you get to see the chops and the fun.
The Scarlet>Fire from Cornell is amazing, for sure.
Try to find a nice, breezy Eyes of the World from when they changed the arrangement, so post '74 (I think anything between '77 and '79 is probably choice), though I love the Grateful Dead Movie version, too, where the changes are a little more abrupt.
I've had a few stops and starts with the Dead, though have been fully invested the last few years. I think also one of the records that got me a little more intrigued, maybe oddly for some, was Without A Net, for a more late-era, jazzy/jammy vibe.
Always loved Branford's sax on this Eyez.