Watercolour or Acrylic to Start With
Both are water-based and that is where the similarity ends. They reward opposite habits.
Watercolour
Transparent and worked light to dark, with the paper providing the white. Corrections are limited, which forces planning. Materials are compact and cleanup is simple.
Acrylic
Opaque, fast drying and forgiving — you can paint over a mistake once it is dry. It works on many surfaces and takes mediums well.
Which is easier
Acrylic is usually more forgiving for a beginner because errors are recoverable. Watercolour is not harder so much as less negotiable.
Do not skimp on paper
With watercolour especially, cheap paper buckles and will not take a wash evenly. Paper quality changes results more than paint quality at the start.