Here are the key differences between 3-legged and 4-legged angular steel towers

Stability - 4-legged towers provide better stability and resistance to lateral loads from wind and uneven terrain. 3-legged towers can require bracing.

Footprint - 4-legged towers have a wider base footprint and spacing between legs for improved support. 3-legged designs occupy less space.

Loading - Weight distribution is more even on 4 legs. 3-legged towers concentrate more load on each leg and foundation.

Height - 4-legged towers can typically reach greater heights while maintaining strength and stability.

Access - Getting access between legs for maintenance can be easier with 3 legs. 4 legs can be more cramped.

Aesthetics - Some may find 3-legged towers more aesthetically pleasing and less visually intrusive.

Cost - 3-legged towers use less material and have simpler foundations, reducing overall cost.

Modularity - 3-legged sections can be more modular for easy transport and assembly. 4-legged sections are heavier.

Redundancy - 4-legged towers offer more redundancy if failure of one leg occurs.

Applications - 4 legs are commonly used for larger transmission towers and in areas prone to high winds. 3 legs for smaller distribution towers.

In summary, 4 legs offer better stability and strength while 3 legs provide more space savings and access. The choice depends on loading, height, cost, and site-specific requirements.