API trading is the best option for retail traders as of now. You can code your own logic and send orders to broker systems. I trade with upstox api using python and automated it end to end. It works fine unless issues from broker side like network issues, volatile day, etc.
Those who are not familiar with coding/programming can take a look at amibroker to nest plugin providers. Recently i have tried one at
www.automaticbuysell.com and its good for those who use amibroker and want to put orders to nest. No coding needed and so I thought of trying it. Only issue i found with them is that orders are processed sequentially and each order placement takes avg around 5 seconds. Good thing is they support all order types like market, stoploss market, limit orders and cover orders.
Last year i tried robotrade as wel but its limited to market orders. It really depends on one’s trading style and strategy and what you want to achieve.