I was only in Puerto Natales for 45 minutes but rather liked this small touristy town one and a half hours south of Torres del Paine National Park. Lots of interesting and quirky architecture, and a nice waterfront.
Had marginally more time to explore Punta Arenas, covering most of the centre city in a couple of hours wandering in the evening. Took advantage of the endless daylight in late December in the most southernly city in the world (or at in least Chile, depending on whether you’d class Ushuaia’s population of 60,000 as a city…). Some impressive architecture dates from the days before the Panama Canal when the Magellan Strait was a busy shipping lane. The city itself was a mix of the modern (cycle lanes, Hotel Dreams), historic (Cathedral, city square), quirky (murals, painted buildings, endless statues) and grotty (most of the rest).