As our business requirement blog is very important on our store ,
running Magento 2 at the moment
which below option is best strategy and better SEO and performance ?
1- Wordpress as CMS , homepage , blog and use Magento as store only
2- Whole website Magento
3- Just use wordpress as blog and Magento on store
4- any other idea?
it really depends on your needs and resources you have.
From our experience it's almost not possible to find good Magento blog module. So in case you want to make everything simple and easy to maintain then it's better to go with a mix of #2 and #3. You can use Fishpig integration module in order to integrate Wordpress blog into Magento. That will allow you to use 90% of Wordpress features in Magento blog. You will also use Wordress admin for blog managment.
In case you have enough resources for your project then i would go with #1. That will reduce resource usage on blog pages and will allow you to use all Wordpress flexibility.