Here's a detailed take on Tsutenkaku based on our family's recommendation:
This retro tower has been Shinsekai's symbol since 1956 (though the original was built in 1912), and our Osaka family says it's like a perfect snapshot of Showa-era Japan. At 103 meters tall, it's not the highest observation deck you'll find, but it's got this charming retro feel that's completely different from modern towers.
What makes it special is the atmosphere around it - the streets below are packed with kushikatsu restaurants and old-school shops that feel frozen in time. The tower itself is delightfully dated, with its mascot Billiken (the "God of Happiness") sitting there with his feet worn shiny from all the people rubbing them for luck.
Inside, each floor has its own character. The observation deck offers 360-degree views of Osaka, but what's really fun are all the retro decorations and displays. There's even this illuminated "Good Luck" spot where locals come to buy fortunes and charms.
Our family says the best time to visit is around sunset - you get to see the city in daylight, then watch all the neon signs come alive in Shinsekai below. Plus, that's when the tower's own neon weather forecast system lights up (different colors indicate tomorrow's weather, a system that's been running since the 50s).
They particularly recommend combining it with dinner at one of the kushikatsu places below - the whole area comes alive at night with locals and visitors mixing together in these tiny restaurants.