I think I'd go for the cage that is not as tall. Heat and humidity keep easier with a shorter cage and royals are terrestrial so there is no need for height.
Sliding or swinging is your choice. I think sliding would be less intrusive if you are tapped for space, but that's the 24" tall cage, and that's even taller than my boa constrictor's cage.
Go for the less expensive model and use the extra cash to deck it out when you want to add features.
Enjoy!!!