Actually a single project might use both techniques successfully.
Wet felting fibres is an ancient craft method used to make items large and small.
Needle felting was devised by industry to felt manmade fibres as the wet method cannot be used. Crafters use needle felting to stiffen felt into 3D shapes. The needle has barbs that catch the individual fibre enabling it to be tangled with other fibres. The technique is very quick, just be careful of the sharp needle point - it hurts!