San Myshuno for me.
I would make apartments more like TS2 apartment life where you can build your own. I'd get rid of the shells and make real neighborhoods with Streets lined with Brownstones, some as apartments, some as whole houses. I'd make it so the highrises acted as retail or businesses on the bottom and apartments/condos on top with way more than 2-4. There should be like at least 20 different living spaces in them. I'd make a big central park area that connects all the different neighborhoods so you can see all of them in the distance when you're there. This area would be off lot and visit-able from any lot in all of San Myshuno. It would have an area near the spice district for food and flea market with basketball hoops and soccer fields, near the art district it would have free dancing classes in the park, murals and places to make your own, free pottery classes, knitting, etc. Near the high rises it would have nice diners and maybe a lake with boat rides. Carriage rides. Wedding venues. Tennis courts. And near the one where the karaoke place is, I'd make it so there is theater in the park or a soundstage where performers come once in a while or where sims put on dancing shows.
I definitely think San Myshuno could have been like an actual city. What we got is just...no.
