What is the best platform to invest in crypto currency in India?

Go with Koinex. It is the best platform to invest. I did investigation of all the bitcoin exchanges in India by creating signup accounts and Koinex is the best among them. Reasons are below:

1. You will be given a special account number to which you can confidently transfer money using imps when you want to invest. This is the biggest usp as you need not transfer to Koinex’s account but only your account designed for you. Transfer of money takes exactly 5 minutes to reflect. There is a minimum amount though which is Rs.2000 you have to transfer.
2. You won’t be charged any money for withdrawing and money directly withdraws to your bank account which you gave during account creation. And this happens instantly
3. KYC process is completely online and takes less than 24 hours to complete
4. I haven’t interacted with customer care, but from what I heard on other quora it is top notch
5. Bitcoin price you see in koinex is less than you see in zebpay or someother exchange. Atleast Rs.10000 difference you can see. Reason for this you can check in koinex site.
6. Koinex has other coins along with bitcoin like litecoin, ripple etc., Good way to diversify your investment.

Bitxoxo also has fast KYC process but their customer support is very bad. I transferred Rs.300 to their account not knowing minimum account is Rs.5000. After raising even 4 tickets they did not refund me the amount. I gave them screenshots, transaction ids everything. With Rs.300 only, they are insincere, consider how much sincere they will be with big amounts. Don’t invest with Bitxoxo.
Coin secure is good, but their tech is way old and KYC, money transfers, buying/selling take time to execute.
Unocoin and Zebpay are good tech wise, but prices of bitcoin are high in them.

Update(31 December, 2017): Due to surge in users, heard from my friends that KYC process of Koinex is taking 3-4 days, and withdrawals are delayed. But Koinex keeps the notices in top of their website whenever you open the website. Please read it before proceeding. Also, Bitcoin rates are fluctuating to be higher than Zebpay due to surge in users. Please exercise your judgement on buying bitcoin in Koinex on whether the price is less than other exchanges.