I started with D&D in late 1979/early 1980. My first adventure was J Eric Holmes' Ruined Tower of Zenopus. That would be my first choice. That and the Great Skull on Stone Mountain. There was not a lot available at the time, but we had B1 and Hommlet (T1). We also had the original White Box and it's supplements, so there was The Temple of the Frog to deal with, then G1-3, D1-3, S1-3, C1 but we weren't high enough level for those. While we waited for T2 the Slavers series oityf A modules started coming out and the Len Lakofka's Lendore Isle L-series.
I think S4 Tsojcanth and WG4 Tharidun naturally follow T1-4 Temple of Elemental Evil and I1 Dwellers of the Forbidden JCity is a nice choice, but I would like to see J Eric Holmes' Zenopus and Skull Mountain, Len Lakofka's Lendore Isle, Dave Arneson's Temple of the Frog and The Slavers and possibly Kill Bargle and Night Below, and maybe The Weavers from Dungeon 138, which follows the Styes in Ghosts of Saltmarsh. Those aren't so classic though