A limited by shares company will be best, particularly if you will be setting up on your own. You will benefit from reduced personal liability for business debts, an enhanced and credible professional image, and a tax efficient structure for paying yourself.
Take a look at this guide for more information on limited by shares companies.
If you are thinking of setting up with other opticians, you also have the option of trading as a limited liability partnership. You will still enjoy limited liability but you will be taxed as a self-employed individual and will have greater flexibility for changing the internal management structure of the business. You can find out more about LLPs here.