Me personally, all my horses either get ridden in a standard loose ring or D-ring snaffle, a rope halter, or a mild curb with short shanks and a solid ported mouth like this.
Most of them go as well in one as the other so it really is a matter of preferance. Usually anything with a smooth mouth will be milder than a rough or twisted mouth. A double joint or barreled snaffle will be milder than a single jointed snaffle. Shorter shanks on a curb with a medium height port are milder than long shanks with either a straight bar mouth or cathedral port.
Bits like the twisted wire and gag bits do have their purpose but 99% of people who use them don't understand the correct time to use them or how to handle them properly and that is one of the reasons why they have such a bad rap. I personally would never use either one but I do know 1 or 2 people who are incredible horsemen that do understand the proper time and horse to use those bits on to get a positive effect with no damage to the mouth.