When comparing different nucleotides, the component that is most variable is the nitrogenous base.
Nucleotides are made up of three components: a phosphate group, a monosaccharide (sugar), and a nitrogenous base. The phosphate group is typically consistent (phosphate in different nucleotides does not vary significantly), and while the sugar can differ slightly (e.g., ribose in RNA versus deoxyribose in DNA), it does not have the same level of variety as the nitrogenous bases.
The nitrogenous bases vary widely in structure and include adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). Each of these bases has a distinct chemical structure, leading to a significant degree of variability.