Compare installation, usable space, access and flexibility. Wall shelves depend on suitable wall construction and secure mounting, while a tall tower has its own base and any anchoring requirements listed by its maker.
Shelves can distribute resting areas across a wall, but they still project into the room and need a connected route. A tower may combine scratching, hiding and sleeping in one item, although its complete footprint can be larger than the base suggests. Think about cleaning and future changes too. Moving a tower may be simpler than relocating several wall-mounted components, while a permanent shelf route can suit a room arranged around it. Neither is automatically better for a large cat. Compare documented loading and usable dimensions for the actual options, then choose the layout that works with your home and the cat's habits.
Consider how often the room changes. A rented room rearranged regularly may favour suitable freestanding furniture, whereas a settled layout may justify fixed shelves. Required anchors and permissions still need checking for either option.
For product comparisons alongside this advice, see SkyRoute wall climbing set and Feline Sovereign Spire. The details below explain their sizes and uses.
Further reading: cats.org.uk; cats.org.uk; cats.org.uk.
SkyRoute wall climbing set
Feline Sovereign Spire