What is the easiest fabric to cross stitch on?

For a beginner, the answer is Aida because it is made of cotton and the holes are evenly spaced and very visible. Aida comes in various counts from 11, 14, 16, 18 and 20 but most recommend 14 Ct (14 holes per inch) for beginners.
 
As stitchers become experienced, many start using even weave fabrics and linen.

olive leaf perforated paper 14 ct