It is not 100% a "smaller is better" choice. You also will want to check whether an instruction depends on an earlier one (for example, the XOR technically needs to read the register; if the CPU does not know that that is not actually the case, a self-XOR may introduce pipeline bubbles), what instruction unit (if any) it uses, and whether you want to preserve flags.
It is not 100% a "smaller is better" choice. You also will want to check whether an instruction depends on an earlier one (for example, the XOR technically needs to read the register; if the CPU does not know that that is not actually the case, a self-XOR may introduce pipeline bubbles), what instruction unit (if any) it uses, and whether you want to preserve flags.