Lot's of choices of internal hubs, with SA or Taiwan introducing a nice selection of hubs including fixed gear 3-speed. Offhand, I don't know of material quality issues with any so it's a wide open field. One consideration is axle width, look for one that matches your frame or has enough axle length to accept spacers, otherwise you'll need to squeeze your rear triangle down a bit (steel only).

Also, and this is opinion only, simpler hubs seem to work and last better, so try to stick to proven, simple hubs like 3 and 5 speed models, rather than trying to get touring type wide gearing with 11 speeds for example. If you need wide gearing, consider building this bike as a city bike, and buying a touring or mtn bike for those applications.