It isn't the bot that is safe, it is what *YOU* tell the bot to do.
Tell the bot to send quality DMs to targeted users, no problem
Tell the bot to spam low quality, flag triggering DMs to people not interested. Problem.
The bot just does what *you* tell it to. Tell it to do stupid things and it will. Use it wisely and you will be fine with any bot you use.
As for best, that depends on what you want to do and how you like to do it. Some are cheaper, some are more expensive, some can do some features others cannot, some are easier to use with less features some have more technical features but more technical to use, some bots offer quality prompt support, others less so.