An India tourist visa (visitor visa) has a validity of 6 months to 10 years. This is a multiple entry visa. Each entry has a limited duration of 6 months.
PIO/OCI has no limits - you can stay as long as you want. That's why PIO/OCI is best. For PIO, if you want to stay more than 180 days, you will be required to register at the police station every month after 180 days. For OCI, you won't be required to register at the police station. For OCI/PIO paperwork, you don't need an employer letter and extra paperwork from India. For work visa, you will need it to work in India and there is limited duration for work visa - for example if your job contract's duration is 6 months, then they will issue 6 months work visa. If your job is a permanent job, I think they give you limited validity visa and you can renew it to extend work visa validity. OCI/PIO benefits are good because it allows you to work at any employer. It is like a green card.
By the way, you cannot use visitor visa to work in India. They will bar you idefinitely from entering India if they find out. Immigration agency is really improving rapidly and becomes very modern (They already computerized the computer system at every immigration control with all data across India) since economy in India is improviing. Also, more immigration agents (including raid agents, border guards, support agents, and inspectors) are hired. Sometimes they check your data on the computer on immigration exit control in India and they would see a red flag. So be careful.