Looking into booking this hotel for December and trying to work out the different categories of room. If I have this right, here are the base level rooms available: Scenic Twin, Scenic King, Signature Twin, Signature King, Scenic Allure King, Signature Allure King.

"Signature" simply means on the 30th-33rd floors and "Scenic" means on the 34th-37th floors. Differences between the non-"Allure" and "Allure" rooms seems to be that the "Allure" rooms are slightly smaller (35-37 sq m vs 40 sq m) and can fit a third person, although the floor plans provided and the fact that an extra bed can fit in the "Allure" room indicates to me that they should be bigger. Not sure if this is a typo or if the non-"Allure" rooms are indeed bigger. For what it's worth, the non-"Allure" King rooms are cheaper than the "Allure" rooms, so maybe they really are bigger.

Either way, it seems to me that the Scenic Allure King would be my preferred room.

https://osakastation-hotel.jp/en/stay/allure-king/
https://osakastation-hotel.jp/en/stay/king/