The term 'best' is subjective when it comes to trading, but here are some popular net credit options strategies:

Popular options strategies for trading with a directional bias:

Bull Put Spread (For a bullish view)
Bear Call Spread (For a bearish view)
Covered Call/Synthetic covered call (Moderately bullish view).
Ratio spreads (Call & Put ratio spreads are used by a few)

Popular options strategies for trading with a neutral bias:

Strangle (Higher tail risk as compared to Iron Condor)
Straddle (Higher tail risk as compared to Iron Butterfly)
Iron Condor (Less tail risk & lower margin requirements)
Iron Butterfly (Less tail risk & lower margin requirements)

Many retail traders prefer naked options selling, thinking they'd get higher credit than credit spread strategy. However, what's most important to note is that credit spreads require far lesser margins than naked shorting, and that can help you in 2 ways:

Your downside risk is protected.
You can enter more prominent positions with the same amount due to the SPAN margin benefit of credit spread strategies.

Here's an example for absolute beginners: If you short Bank Nifty 38000CE that expires on 20th Jan, you will require a margin of 1.42 lacs. You'd receive a total credit of 190*25 = 4750. (Max ROI = 3.3%) However, if you converted it to a bull put spread strategy by simply purchasing a further away OTM put option at strike price 37000 at 28, you'd require approx. 42,000 as margin and you'd receive a net credit of 162*25 = 4050 (Max ROI = 9.6%).

You can also do 3 lots for the a lesser amount compared to a naked short. So that means your max return could potentially be 4050*3 = 12,150.

The BEST strategy for YOU depends on your ability to withstand risks, expected returns, view on the market, and your trading timeframe.

Which are the best 'Net Credit' options strategies for Nifty & BankNifty?