Gang, this is our favorite for a 914-6 (original equipment) or a 914-4 that originally came with the 17mm units. This unit is less expensive than the stock ATE 17mm master cylinder and it will give you a slightly firmer pedal.
We're not fans of the Chinese import master cylinders out there as of yet. They'll go by names like Hamburg-Technic (slick). There's been too many failures for us to recommend or sell them. If others are charging over $75 for that stuff, you're getting ripped off. If it's less than our prices, it's probably not ATE.
Our stance today: Use original ATE master cylinders. The others may have better QC in the future but for now... brakes are an important part of your "staying alive" plan.