Choosing what type of dropouts you’d like on your custom handmade bicycle frame can be a bit daunting. There are a lot of choices out there. You need to first decide what type of drivetrain you want to ride whether it be strictly single speed, geared, or the ability to run both.
Walt of Waltworks Bicycles has a really nice article detailing his thoughts on the many dropout choices available. He’s built a ton of high quality bikes so I think his experience is very helpful in trying to decide what dropout setup might be right for you. Be sure to thoroughly discuss this topic with you own custom builder because they may have their own opinions and have familiarity with certain dropouts over others.