Salsa is most definitely easier. It is a standard 8 count, devided into two separate beats of four. The basic stays the same throughout.
Tango on the other hand changes. There are two different types - Argentinian and strict Ballroom Tango. Ballroom is very strict syllabus driven, where Argentinian is a street dance - which has been adapted to the dancing scene - just like Salsa.
Salsa - party dance
Tango - Passion and feeling.
Its actually not about what is easier, its what your soul will grasp better - your own personal choice.