Is this cheating? The Last Story only has one town.
Another one that might not count. The slavepens from Dark Sun: Shattered Lands. Not an actual town, but it is a starting area that you and other people live in and you're free to explore. You're also free to fight stronger and stronger enemies in the area, try various schemes to escape, murder all the guards, murder all the other slaves, find treasure, and help a few people out.
Not the starting city, but the first you come to I guess. Balmora in Morrowind. So much stuff going on in this city with the imperial fort just outside, the thief guild, the quest guy, the mines, all the rumours about awakening or whatever it was. Simplly makes you incredibly intrigued to continue the game.
Yharnam is amazing, but it's not really a "town" in the RPG sense though, I'd say. I don't know if the OP meant to include towns that are dungeons/combat areas or just "safe" places with safe NPC interactions and whatnot.
Had to think about it for a minute and go through a few RPGs until I realised Athkatla exists. Not only is it a starting town but it also happen to stretch out over several zones, it's also huge and I don't think any other game I can come up with would even compete as far as I'm concerned. In second place I would say Easthaven from Icewind dale. The snowy atmosphere made me want to cuddle down in front of a fire each time I played it.