If your savings meet the requirements (at least £62,500 held in full in an account in your name(s) for at least 6 months), you definitely want to use savings.
Cash savings is the easiest category to apply under and should be your first option... all you need to do is provide 6 full months of bank statements, plus a declaration of the source of the savings.
Self-employment at as a Director of a Limited Company is the most difficult category to apply under, because so many documents are needed, you can only use income from the last full financial year, and it's easy to get something wrong.
You only want to use your self-employment as an absolute last resort if you really cannot meet the requirements under any other category.