For me on most characters it is a 10. If I am playing a Rune Knight it is usually a 14, on Clerics, Fighters and Rangers I expect to be in melee a lot it is typically a 12. Bards, Rogues, Wizards (including Bladesingers), Sorcerers, Warlocks and non melee Clerics, Fighters and Rangers usually a 10.
I don't generally play Barbarians, Druids, Artificers or Paladins.
I have rolled up 5E characters with a 15-18 Constitution, but I don't think I have ever played one on point buy and I don't think I ever put an ASI towards con (although I did plus up an odd con with a half feat once). There has to be a really compelling reason for me to put points into con, because it is by far the least useful ability in two of the three pillars of the game.
My recent/current PCs:
Zeek - Scout 7/Twilight Cleric 2 - 10
Tazzi - Bladesinger 10/Arcane Trickster 4 - 12 (rolled stats)
Xane 1 - Arcane Trickster 4/Fighter 2 - 10
Xane 2 - Arcane Trickster 3/Shadow Sorcerer 1/Fighter 2 - 10
Isi - Rogue 1/Rune Knight 5 - 14
Chromescale - Fey Wanderer Ranger 8/Whispers Bard 4 - 10 (19 with amulet of health)
Jexri - Bladesinger 9/Undead Warlock 2 - 10
Rinn - Monk 1/Bladesinger 2 - 10 (score at the time of her death)
Midnight - Undead Warlock 5/Shadow Sorcerer 1 - 14 (rolled stats)
Dezi - Tempest Cleric 6/Fathomless Warlock 1 - 12
Jia - Wizard 1/Undead Warlock 1 - 10
Afelia - Bladesinger 8 - 12 (rolled stats)
Taslania - Fighter 6/Hexblade 2 - 15 (rolled stats)
Jim - Swashbuckler 5/Ranger 1 - 14 (rolled stats)
Leena - Rogue 1/Fey Wanderer 14 - 10