I personally prefer the bots that I can create and customize by myself. Bots don't have brains. You are on your own have to put a strategy inside the bot and the bot will perform in the way you have told it. I had some experience with some platforms, some were good some were total disasters.
I use a platform called Cleo one where you can create your strategies by type such as:
When Price is crossing up EMA (20) then BUY ETH/USDVolume:15% of the portfolio balance, Stop Loss:8% of market price, Trailing Take Profit:20% of the market price (Trailing:3% of market price)then close if Price is crossing down EMA (20)
Then I can backtest, paper trade them and live to trade them if I will be convinced enough. What I like is, they have lots of indicators, candlestick patterns, % volume and price changes, availability of trailing stop loss/take profit, easy to use, you can create your strategies in low time frames as well as daily and hourly ones, useful statistics. You can place manual trade on your own if you would prefer. As for downsides, I would say, they have limited support of exchanges. Currently, they have binance, binance us, coinbasepro, bitpandapro, hitbtc and bitfinex.
You brought a very important topic that most people never talk about and that is backtesting our strategy, most people use strategies that they do not really know if they actually work and this makes them to make mistakes that they would have not otherwise made if they knew what they were doing, this is why it is important to test any strategy by paper trading before we actually use it in the market or we run the risk of losing our money with an untested strategy.