O visa is definitely better than OA as you have to buy mandatory health insurance.on renewal of OA. The health insurance could be increasingly costly with advancing age and does not offer protection for pre existing health problem, also most company do not accept applicants over 65
don't forget an OA visa requires you to buy annually mandatory health insurance which gets expensive with advancing age (O visa does not require health insurancr) As health insurance does not cover all pre existing health problems, so it is not very helpful protection but simply used to satisfy OA visa requirement
better apply O visa instead coz you need to pay annual mandatory expensive health insurance to renew your OA but your pre existing illness is not covered
if you can better change to non O VISA, it does not require buying costly but not quite useful health insurance as all pre existing health problem not covered